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 $148.85   11.342%   $165.7326   $165.73   $165.75   $165.70  
  Purchase #2 $120.63   13.320%   $136.6979   $136.70   $136.70   $136.70  
  Purchase #3 $120.87   6.360%   $128.5573   $128.56   $128.55   $128.60  
  Purchase #4 $245.26   8.556%   $266.2444   $266.24   $266.25   $266.20  
  Purchase #5 $193.64   13.401%   $219.5897   $219.59   $219.60   $219.60  
  Purchase #6 $71.77   5.162%   $75.4748   $75.47   $75.45   $75.50  
  Purchase #7 $25.72   10.277%   $28.3632   $28.36   $28.35   $28.40  
  7 purchase totals = $926.74       $1,020.6599   $1,020.65   $1,020.65   $1,020.70