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 $187.87   3.347%   $194.158   $194.16   $194.15   $194.20  
  Purchase #2 $88.82   12.630%   $100.038   $100.04   $100.05   $100.00  
  Purchase #3 $178.41   13.720%   $202.8879   $202.89   $202.90   $202.90  
  Purchase #4 $113.30   13.477%   $128.5694   $128.57   $128.55   $128.60  
  Purchase #5 $155.91   13.499%   $176.9563   $176.96   $176.95   $177.00  
  Purchase #6 $104.27   10.786%   $115.5166   $115.52   $115.50   $115.50  
  Purchase #7 $112.59   3.651%   $116.7007   $116.70   $116.70   $116.70  
  7 purchase totals = $941.17       $1,034.8269   $1,034.84   $1,034.80   $1,034.90