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 $203.86   13.461%   $231.3016   $231.30   $231.30   $231.30  
  Purchase #2 $94.83   11.412%   $105.652   $105.65   $105.65   $105.70  
  Purchase #3 $129.73   6.561%   $138.2416   $138.24   $138.25   $138.20  
  Purchase #4 $220.97   6.781%   $235.954   $235.95   $235.95   $236.00  
  Purchase #5 $118.39   7.709%   $127.5167   $127.52   $127.50   $127.50  
  Purchase #6 $45.76   10.110%   $50.3863   $50.39   $50.40   $50.40  
  Purchase #7 $148.43   11.579%   $165.6167   $165.62   $165.60   $165.60  
  7 purchase totals = $961.97       $1,054.6689   $1,054.67   $1,054.65   $1,054.70