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 $62.92   7.418%   $67.5874   $67.59   $67.60   $67.60  
  Purchase #2 $176.30   8.797%   $191.8091   $191.81   $191.80   $191.80  
  Purchase #3 $94.35   12.794%   $106.4211   $106.42   $106.40   $106.40  
  Purchase #4 $25.94   10.305%   $28.6131   $28.61   $28.60   $28.60  
  Purchase #5 $21.43   6.220%   $22.7629   $22.76   $22.75   $22.80  
  Purchase #6 $87.98   11.740%   $98.3089   $98.31   $98.30   $98.30  
  Purchase #7 $47.34   8.117%   $51.1826   $51.18   $51.20   $51.20  
  7 purchase totals = $516.26       $566.6851   $566.68   $566.65   $566.70