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 $61.43   11.535%   $68.516   $68.52   $68.50   $68.50  
  Purchase #2 $39.79   4.814%   $41.7055   $41.71   $41.70   $41.70  
  Purchase #3 $61.52   11.152%   $68.3807   $68.38   $68.40   $68.40  
  Purchase #4 $106.37   6.765%   $113.5659   $113.57   $113.55   $113.60  
  Purchase #5 $141.78   5.804%   $150.0089   $150.01   $150.00   $150.00  
  Purchase #6 $201.94   5.702%   $213.4546   $213.45   $213.45   $213.50  
  Purchase #7 $169.94   6.594%   $181.1458   $181.15   $181.15   $181.10  
  7 purchase totals = $782.77       $836.7774   $836.79   $836.75   $836.80