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 $7.46   10.339%   $8.2313   $8.23   $8.25   $8.20  
  Purchase #2 $203.34   11.854%   $227.4439   $227.44   $227.45   $227.40  
  Purchase #3 $181.60   11.277%   $202.079   $202.08   $202.10   $202.10  
  Purchase #4 $166.30   12.840%   $187.6529   $187.65   $187.65   $187.70  
  Purchase #5 $186.61   8.403%   $202.2908   $202.29   $202.30   $202.30  
  Purchase #6 $22.38   8.714%   $24.3302   $24.33   $24.35   $24.30  
  Purchase #7 $110.65   8.408%   $119.9535   $119.95   $119.95   $120.00  
  7 purchase totals = $878.34       $971.9816   $971.97   $972.05   $972.00