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 $194.41   3.503%   $201.2202   $201.22   $201.20   $201.20  
  Purchase #2 $115.34   4.778%   $120.8509   $120.85   $120.85   $120.90  
  Purchase #3 $107.98   7.770%   $116.37   $116.37   $116.35   $116.40  
  Purchase #4 $8.45   6.755%   $9.0208   $9.02   $9.00   $9.00  
  Purchase #5 $55.38   8.806%   $60.2568   $60.26   $60.25   $60.30  
  Purchase #6 $80.49   10.380%   $88.8449   $88.84   $88.85   $88.80  
  Purchase #7 $151.56   10.745%   $167.8451   $167.85   $167.85   $167.80  
  7 purchase totals = $713.61       $764.4087   $764.41   $764.35   $764.40