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 $204.66   9.219%   $223.5276   $223.53   $223.55   $223.50  
  Purchase #2 $231.39   10.258%   $255.126   $255.13   $255.15   $255.10  
  Purchase #3 $224.51   11.126%   $249.489   $249.49   $249.50   $249.50  
  Purchase #4 $67.87   5.374%   $71.5173   $71.52   $71.50   $71.50  
  Purchase #5 $110.98   7.801%   $119.6375   $119.64   $119.65   $119.60  
  Purchase #6 $188.35   10.230%   $207.6182   $207.62   $207.60   $207.60  
  Purchase #7 $224.91   7.379%   $241.5061   $241.51   $241.50   $241.50  
  7 purchase totals = $1,252.67       $1,368.4217   $1,368.44   $1,368.45   $1,368.30