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 $214.93   9.357%   $235.041   $235.04   $235.05   $235.00  
  Purchase #2 $19.39   12.232%   $21.7618   $21.76   $21.75   $21.80  
  Purchase #3 $118.54   13.251%   $134.2477   $134.25   $134.25   $134.20  
  Purchase #4 $182.59   10.804%   $202.317   $202.32   $202.30   $202.30  
  Purchase #5 $95.91   7.347%   $102.9565   $102.96   $102.95   $103.00  
  Purchase #6 $198.42   13.251%   $224.7126   $224.71   $224.70   $224.70  
  Purchase #7 $85.88   13.569%   $97.5331   $97.53   $97.55   $97.50  
  7 purchase totals = $915.66       $1,018.5697   $1,018.57   $1,018.55   $1,018.50