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 $182.48   6.821%   $194.927   $194.93   $194.95   $194.90  
  Purchase #2 $110.44   6.490%   $117.6076   $117.61   $117.60   $117.60  
  Purchase #3 $133.41   6.574%   $142.1804   $142.18   $142.20   $142.20  
  Purchase #4 $238.56   5.438%   $251.5329   $251.53   $251.55   $251.50  
  Purchase #5 $84.35   5.873%   $89.3039   $89.30   $89.30   $89.30  
  Purchase #6 $129.32   8.310%   $140.0665   $140.07   $140.05   $140.10  
  Purchase #7 $14.45   3.820%   $15.002   $15.00   $15.00   $15.00  
  7 purchase totals = $893.01       $950.6203   $950.62   $950.65   $950.60