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 $44.98   3.167%   $46.4045   $46.40   $46.40   $46.40  
  Purchase #2 $19.79   12.339%   $22.2319   $22.23   $22.25   $22.20  
  Purchase #3 $239.34   5.603%   $252.7502   $252.75   $252.75   $252.80  
  Purchase #4 $73.26   3.766%   $76.019   $76.02   $76.00   $76.00  
  Purchase #5 $8.87   10.847%   $9.8321   $9.83   $9.85   $9.80  
  Purchase #6 $188.91   8.104%   $204.2193   $204.22   $204.20   $204.20  
  Purchase #7 $174.83   3.650%   $181.2113   $181.21   $181.20   $181.20  
  7 purchase totals = $749.98       $792.6683   $792.66   $792.65   $792.60