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 $52.56   12.220%   $58.9828   $58.98   $59.00   $59.00  
  Purchase #2 $194.27   4.274%   $202.5731   $202.57   $202.55   $202.60  
  Purchase #3 $152.47   13.333%   $172.7988   $172.80   $172.80   $172.80  
  Purchase #4 $33.29   11.344%   $37.0664   $37.07   $37.05   $37.10  
  Purchase #5 $110.47   10.695%   $122.2848   $122.28   $122.30   $122.30  
  Purchase #6 $88.97   7.626%   $95.7549   $95.75   $95.75   $95.80  
  Purchase #7 $248.73   12.764%   $280.4779   $280.48   $280.50   $280.50  
  7 purchase totals = $880.76       $969.9387   $969.93   $969.95   $970.10