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 $214.60   8.138%   $232.0641   $232.06   $232.05   $232.10  
  Purchase #2 $95.50   12.748%   $107.6743   $107.67   $107.65   $107.70  
  Purchase #3 $28.90   7.308%   $31.012   $31.01   $31.00   $31.00  
  Purchase #4 $204.28   13.443%   $231.7414   $231.74   $231.75   $231.70  
  Purchase #5 $67.94   9.712%   $74.5383   $74.54   $74.55   $74.50  
  Purchase #6 $174.92   11.332%   $194.7419   $194.74   $194.75   $194.70  
  Purchase #7 $55.27   8.509%   $59.9729   $59.97   $59.95   $60.00  
  7 purchase totals = $841.41       $931.7449   $931.73   $931.70   $931.70