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 $233.80   7.359%   $251.0053   $251.01   $251.00   $251.00  
  Purchase #2 $191.71   12.445%   $215.5683   $215.57   $215.55   $215.60  
  Purchase #3 $48.58   3.566%   $50.3124   $50.31   $50.30   $50.30  
  Purchase #4 $84.59   5.701%   $89.4125   $89.41   $89.40   $89.40  
  Purchase #5 $229.34   11.123%   $254.8495   $254.85   $254.85   $254.80  
  Purchase #6 $70.98   5.634%   $74.979   $74.98   $75.00   $75.00  
  Purchase #7 $84.67   13.292%   $95.9243   $95.92   $95.90   $95.90  
  7 purchase totals = $943.67       $1,032.0513   $1,032.05   $1,032.00   $1,032.00