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 $64.90   13.785%   $73.8465   $73.85   $73.85   $73.80  
  Purchase #2 $131.52   9.131%   $143.5291   $143.53   $143.55   $143.50  
  Purchase #3 $174.66   5.415%   $184.1178   $184.12   $184.10   $184.10  
  Purchase #4 $143.31   11.775%   $160.1848   $160.18   $160.20   $160.20  
  Purchase #5 $140.54   6.695%   $149.9492   $149.95   $149.95   $149.90  
  Purchase #6 $168.57   8.529%   $182.9473   $182.95   $182.95   $182.90  
  Purchase #7 $223.87   3.646%   $232.0323   $232.03   $232.05   $232.00  
  7 purchase totals = $1,047.37       $1,126.6070   $1,126.61   $1,126.65   $1,126.40