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 $237.57   12.599%   $267.5014   $267.50   $267.50   $267.50  
  Purchase #2 $76.59   9.286%   $83.7021   $83.70   $83.70   $83.70  
  Purchase #3 $17.94   3.139%   $18.5031   $18.50   $18.50   $18.50  
  Purchase #4 $211.84   13.370%   $240.163   $240.16   $240.15   $240.20  
  Purchase #5 $147.92   3.198%   $152.6505   $152.65   $152.65   $152.70  
  Purchase #6 $188.42   7.267%   $202.1125   $202.11   $202.10   $202.10  
  Purchase #7 $47.27   7.371%   $50.7543   $50.75   $50.75   $50.80  
  7 purchase totals = $927.55       $1,015.3869   $1,015.37   $1,015.35   $1,015.50