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 $60.49   9.131%   $66.0133   $66.01   $66.00   $66.00  
  Purchase #2 $46.83   12.420%   $52.6463   $52.65   $52.65   $52.60  
  Purchase #3 $25.90   3.588%   $26.8293   $26.83   $26.85   $26.80  
  Purchase #4 $210.31   4.592%   $219.9674   $219.97   $219.95   $220.00  
  Purchase #5 $112.29   8.286%   $121.5943   $121.59   $121.60   $121.60  
  Purchase #6 $8.78   7.633%   $9.4502   $9.45   $9.45   $9.50  
  Purchase #7 $101.37   4.415%   $105.8455   $105.85   $105.85   $105.80  
  7 purchase totals = $565.97       $602.3463   $602.35   $602.35   $602.30