Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $216.75   10.115%   $238.6743   $238.67   $238.65   $238.70  
  Purchase #2 $248.39   12.166%   $278.6091   $278.61   $278.60   $278.60  
  Purchase #3 $87.45   10.551%   $96.6768   $96.68   $96.70   $96.70  
  Purchase #4 $166.86   10.279%   $184.0115   $184.01   $184.00   $184.00  
  Purchase #5 $232.65   9.393%   $254.5028   $254.50   $254.50   $254.50  
  Purchase #6 $170.78   12.435%   $192.0165   $192.02   $192.00   $192.00  
  Purchase #7 $188.35   11.654%   $210.3003   $210.30   $210.30   $210.30  
  7 purchase totals = $1,311.23       $1,454.7913   $1,454.79   $1,454.75   $1,454.80