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 $235.94   11.186%   $262.3322   $262.33   $262.35   $262.30  
  Purchase #2 $87.59   5.535%   $92.4381   $92.44   $92.45   $92.40  
  Purchase #3 $62.51   5.623%   $66.0249   $66.02   $66.00   $66.00  
  Purchase #4 $202.41   11.479%   $225.6446   $225.64   $225.65   $225.60  
  Purchase #5 $103.27   5.506%   $108.956   $108.96   $108.95   $109.00  
  Purchase #6 $113.95   13.457%   $129.2843   $129.28   $129.30   $129.30  
  Purchase #7 $48.89   13.159%   $55.3234   $55.32   $55.30   $55.30  
  7 purchase totals = $854.56       $940.0035   $939.99   $940.00   $939.90