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 $195.49   6.323%   $207.8508   $207.85   $207.85   $207.90  
  Purchase #2 $33.69   12.277%   $37.8261   $37.83   $37.85   $37.80  
  Purchase #3 $110.38   6.467%   $117.5183   $117.52   $117.50   $117.50  
  Purchase #4 $58.90   8.659%   $64.0002   $64.00   $64.00   $64.00  
  Purchase #5 $179.38   6.237%   $190.5679   $190.57   $190.55   $190.60  
  Purchase #6 $226.96   3.582%   $235.0897   $235.09   $235.10   $235.10  
  Purchase #7 $68.87   7.646%   $74.1358   $74.14   $74.15   $74.10  
  7 purchase totals = $873.67       $926.9888   $927.00   $927.00   $927.00