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 $175.87   4.770%   $184.259   $184.26   $184.25   $184.30  
  Purchase #2 $86.78   6.408%   $92.3409   $92.34   $92.35   $92.30  
  Purchase #3 $150.87   12.192%   $169.2641   $169.26   $169.25   $169.30  
  Purchase #4 $84.73   5.462%   $89.358   $89.36   $89.35   $89.40  
  Purchase #5 $108.87   11.616%   $121.5163   $121.52   $121.50   $121.50  
  Purchase #6 $113.65   3.745%   $117.9062   $117.91   $117.90   $117.90  
  Purchase #7 $246.28   5.661%   $260.2219   $260.22   $260.20   $260.20  
  7 purchase totals = $967.05       $1,034.8664   $1,034.87   $1,034.80   $1,034.90