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 $60.27   7.136%   $64.5709   $64.57   $64.55   $64.60  
  Purchase #2 $228.47   11.594%   $254.9588   $254.96   $254.95   $255.00  
  Purchase #3 $73.65   10.555%   $81.4238   $81.42   $81.40   $81.40  
  Purchase #4 $160.70   12.636%   $181.0061   $181.01   $181.00   $181.00  
  Purchase #5 $104.40   9.681%   $114.507   $114.51   $114.50   $114.50  
  Purchase #6 $156.71   9.660%   $171.8482   $171.85   $171.85   $171.80  
  Purchase #7 $241.69   4.350%   $252.2035   $252.20   $252.20   $252.20  
  7 purchase totals = $1,025.89       $1,120.5183   $1,120.52   $1,120.45   $1,120.50