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 $82.56   12.838%   $93.1591   $93.16   $93.15   $93.20  
  Purchase #2 $119.62   9.765%   $131.3009   $131.30   $131.30   $131.30  
  Purchase #3 $159.98   6.483%   $170.3515   $170.35   $170.35   $170.40  
  Purchase #4 $26.64   9.873%   $29.2702   $29.27   $29.25   $29.30  
  Purchase #5 $167.45   12.592%   $188.5353   $188.54   $188.55   $188.50  
  Purchase #6 $232.30   6.426%   $247.2276   $247.23   $247.25   $247.20  
  Purchase #7 $130.54   3.566%   $135.1951   $135.20   $135.20   $135.20  
  7 purchase totals = $919.09       $995.0397   $995.05   $995.05   $995.10