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 $61.75   10.632%   $68.3153   $68.32   $68.30   $68.30  
  Purchase #2 $240.28   13.347%   $272.3502   $272.35   $272.35   $272.40  
  Purchase #3 $189.80   10.865%   $210.4218   $210.42   $210.40   $210.40  
  Purchase #4 $77.89   12.384%   $87.5359   $87.54   $87.55   $87.50  
  Purchase #5 $184.66   11.781%   $206.4148   $206.41   $206.40   $206.40  
  Purchase #6 $34.72   12.404%   $39.0267   $39.03   $39.05   $39.00  
  Purchase #7 $46.33   10.128%   $51.0223   $51.02   $51.00   $51.00  
  7 purchase totals = $835.43       $935.0870   $935.09   $935.05   $935.00