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 $82.32   11.642%   $91.9037   $91.90   $91.90   $91.90  
  Purchase #2 $165.84   5.693%   $175.2813   $175.28   $175.30   $175.30  
  Purchase #3 $77.92   9.750%   $85.5172   $85.52   $85.50   $85.50  
  Purchase #4 $203.42   10.611%   $225.0049   $225.00   $225.00   $225.00  
  Purchase #5 $229.93   13.640%   $261.2925   $261.29   $261.30   $261.30  
  Purchase #6 $47.34   7.565%   $50.9213   $50.92   $50.90   $50.90  
  Purchase #7 $153.94   6.385%   $163.7691   $163.77   $163.75   $163.80  
  7 purchase totals = $960.71       $1,053.6900   $1,053.68   $1,053.65   $1,053.70