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 $42.60   4.808%   $44.6482   $44.65   $44.65   $44.60  
  Purchase #2 $61.78   9.786%   $67.8258   $67.83   $67.85   $67.80  
  Purchase #3 $182.66   6.731%   $194.9548   $194.95   $194.95   $195.00  
  Purchase #4 $147.44   5.195%   $155.0995   $155.10   $155.10   $155.10  
  Purchase #5 $231.65   9.864%   $254.5   $254.50   $254.50   $254.50  
  Purchase #6 $19.59   13.222%   $22.1802   $22.18   $22.20   $22.20  
  Purchase #7 $23.33   7.651%   $25.115   $25.12   $25.10   $25.10  
  7 purchase totals = $709.05       $764.3235   $764.33   $764.35   $764.30