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 $59.56   3.529%   $61.6619   $61.66   $61.65   $61.70  
  Purchase #2 $84.84   9.346%   $92.7691   $92.77   $92.75   $92.80  
  Purchase #3 $116.85   4.120%   $121.6642   $121.66   $121.65   $121.70  
  Purchase #4 $170.85   4.769%   $178.9978   $179.00   $179.00   $179.00  
  Purchase #5 $16.41   6.113%   $17.4131   $17.41   $17.40   $17.40  
  Purchase #6 $112.73   11.162%   $125.3129   $125.31   $125.30   $125.30  
  Purchase #7 $97.74   6.810%   $104.3961   $104.40   $104.40   $104.40  
  7 purchase totals = $658.98       $702.2151   $702.21   $702.15   $702.30