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 $223.71   10.819%   $247.9132   $247.91   $247.90   $247.90  
  Purchase #2 $214.87   10.745%   $237.9578   $237.96   $237.95   $238.00  
  Purchase #3 $43.80   6.466%   $46.6321   $46.63   $46.65   $46.60  
  Purchase #4 $49.52   12.229%   $55.5758   $55.58   $55.60   $55.60  
  Purchase #5 $92.31   7.486%   $99.2203   $99.22   $99.20   $99.20  
  Purchase #6 $196.73   3.760%   $204.127   $204.13   $204.15   $204.10  
  Purchase #7 $67.34   3.750%   $69.8653   $69.87   $69.85   $69.90  
  7 purchase totals = $888.28       $961.2915   $961.30   $961.30   $961.30