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 $52.34   12.578%   $58.9233   $58.92   $58.90   $58.90  
  Purchase #2 $111.81   13.195%   $126.5633   $126.56   $126.55   $126.60  
  Purchase #3 $186.66   7.817%   $201.2512   $201.25   $201.25   $201.30  
  Purchase #4 $91.56   9.721%   $100.4605   $100.46   $100.45   $100.50  
  Purchase #5 $233.98   10.625%   $258.8404   $258.84   $258.85   $258.80  
  Purchase #6 $243.37   12.816%   $274.5603   $274.56   $274.55   $274.60  
  Purchase #7 $114.49   9.189%   $125.0105   $125.01   $125.00   $125.00  
  7 purchase totals = $1,034.21       $1,145.6095   $1,145.60   $1,145.55   $1,145.70