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 $231.42   5.457%   $244.0486   $244.05   $244.05   $244.00  
  Purchase #2 $58.61   12.581%   $65.9837   $65.98   $66.00   $66.00  
  Purchase #3 $64.72   7.775%   $69.752   $69.75   $69.75   $69.80  
  Purchase #4 $150.94   9.656%   $165.5148   $165.51   $165.50   $165.50  
  Purchase #5 $25.97   9.851%   $28.5283   $28.53   $28.55   $28.50  
  Purchase #6 $185.82   3.570%   $192.4538   $192.45   $192.45   $192.50  
  Purchase #7 $184.53   10.573%   $204.0404   $204.04   $204.05   $204.00  
  7 purchase totals = $902.01       $970.3216   $970.31   $970.35   $970.30