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 $32.92   8.305%   $35.654   $35.65   $35.65   $35.70  
  Purchase #2 $98.39   5.635%   $103.9343   $103.93   $103.95   $103.90  
  Purchase #3 $82.57   10.627%   $91.3447   $91.34   $91.35   $91.30  
  Purchase #4 $241.53   8.748%   $262.659   $262.66   $262.65   $262.70  
  Purchase #5 $62.54   3.688%   $64.8465   $64.85   $64.85   $64.80  
  Purchase #6 $132.56   10.485%   $146.4589   $146.46   $146.45   $146.50  
  Purchase #7 $55.28   12.351%   $62.1076   $62.11   $62.10   $62.10  
  7 purchase totals = $705.79       $767.0050   $767.00   $767.00   $767.00