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 $56.40   3.850%   $58.5714   $58.57   $58.55   $58.60  
  Purchase #2 $219.71   4.827%   $230.3154   $230.32   $230.30   $230.30  
  Purchase #3 $93.28   4.467%   $97.4468   $97.45   $97.45   $97.40  
  Purchase #4 $109.92   10.793%   $121.7837   $121.78   $121.80   $121.80  
  Purchase #5 $56.72   11.406%   $63.1895   $63.19   $63.20   $63.20  
  Purchase #6 $170.81   6.747%   $182.3346   $182.33   $182.35   $182.30  
  Purchase #7 $65.42   8.232%   $70.8054   $70.81   $70.80   $70.80  
  7 purchase totals = $772.26       $824.4468   $824.45   $824.45   $824.40