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 $146.56   12.821%   $165.3505   $165.35   $165.35   $165.40  
  Purchase #2 $184.49   13.644%   $209.6618   $209.66   $209.65   $209.70  
  Purchase #3 $9.48   7.525%   $10.1934   $10.19   $10.20   $10.20  
  Purchase #4 $161.98   5.605%   $171.059   $171.06   $171.05   $171.10  
  Purchase #5 $211.92   8.749%   $230.4609   $230.46   $230.45   $230.50  
  Purchase #6 $87.89   10.181%   $96.8381   $96.84   $96.85   $96.80  
  Purchase #7 $241.34   13.389%   $273.653   $273.65   $273.65   $273.70  
  7 purchase totals = $1,043.66       $1,157.2167   $1,157.21   $1,157.20   $1,157.40