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 $93.79   9.576%   $102.7713   $102.77   $102.75   $102.80  
  Purchase #2 $226.75   7.229%   $243.1418   $243.14   $243.15   $243.10  
  Purchase #3 $61.57   9.102%   $67.1741   $67.17   $67.15   $67.20  
  Purchase #4 $213.27   5.198%   $224.3558   $224.36   $224.35   $224.40  
  Purchase #5 $94.87   3.502%   $98.1923   $98.19   $98.20   $98.20  
  Purchase #6 $139.26   8.239%   $150.7336   $150.73   $150.75   $150.70  
  Purchase #7 $118.29   5.238%   $124.486   $124.49   $124.50   $124.50  
  7 purchase totals = $947.80       $1,010.8549   $1,010.85   $1,010.85   $1,010.90