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 $96.31   6.258%   $102.3371   $102.34   $102.35   $102.30  
  Purchase #2 $158.46   12.190%   $177.7763   $177.78   $177.80   $177.80  
  Purchase #3 $12.60   7.690%   $13.5689   $13.57   $13.55   $13.60  
  Purchase #4 $229.30   6.868%   $245.0483   $245.05   $245.05   $245.00  
  Purchase #5 $206.87   3.184%   $213.4567   $213.46   $213.45   $213.50  
  Purchase #6 $192.59   9.350%   $210.5972   $210.60   $210.60   $210.60  
  Purchase #7 $52.84   3.759%   $54.8263   $54.83   $54.85   $54.80  
  7 purchase totals = $948.97       $1,017.6108   $1,017.63   $1,017.65   $1,017.60