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 $235.48   13.507%   $267.2863   $267.29   $267.30   $267.30  
  Purchase #2 $57.91   3.230%   $59.7805   $59.78   $59.80   $59.80  
  Purchase #3 $204.84   9.270%   $223.8287   $223.83   $223.85   $223.80  
  Purchase #4 $201.63   11.649%   $225.1179   $225.12   $225.10   $225.10  
  Purchase #5 $57.89   4.455%   $60.469   $60.47   $60.45   $60.50  
  Purchase #6 $6.86   9.435%   $7.5072   $7.51   $7.50   $7.50  
  Purchase #7 $195.75   7.154%   $209.754   $209.75   $209.75   $209.80  
  7 purchase totals = $960.36       $1,053.7436   $1,053.75   $1,053.75   $1,053.80