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 $89.72   6.541%   $95.5886   $95.59   $95.60   $95.60  
  Purchase #2 $94.62   10.582%   $104.6327   $104.63   $104.65   $104.60  
  Purchase #3 $77.37   7.558%   $83.2176   $83.22   $83.20   $83.20  
  Purchase #4 $234.45   11.682%   $261.8384   $261.84   $261.85   $261.80  
  Purchase #5 $198.91   10.427%   $219.6503   $219.65   $219.65   $219.70  
  Purchase #6 $80.48   4.175%   $83.84   $83.84   $83.85   $83.80  
  Purchase #7 $139.64   12.761%   $157.4595   $157.46   $157.45   $157.50  
  7 purchase totals = $915.19       $1,006.2271   $1,006.23   $1,006.25   $1,006.20