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 $188.49   4.513%   $196.9966   $197.00   $197.00   $197.00  
  Purchase #2 $118.66   8.299%   $128.5076   $128.51   $128.50   $128.50  
  Purchase #3 $53.60   4.412%   $55.9648   $55.96   $55.95   $56.00  
  Purchase #4 $194.46   6.357%   $206.8218   $206.82   $206.80   $206.80  
  Purchase #5 $97.29   5.522%   $102.6624   $102.66   $102.65   $102.70  
  Purchase #6 $194.37   4.494%   $203.105   $203.11   $203.10   $203.10  
  Purchase #7 $143.50   13.226%   $162.4793   $162.48   $162.50   $162.50  
  7 purchase totals = $990.37       $1,056.5375   $1,056.54   $1,056.50   $1,056.60