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 $108.99   9.729%   $119.5936   $119.59   $119.60   $119.60  
  Purchase #2 $232.53   8.348%   $251.9416   $251.94   $251.95   $251.90  
  Purchase #3 $219.96   9.204%   $240.2051   $240.21   $240.20   $240.20  
  Purchase #4 $59.97   12.126%   $67.242   $67.24   $67.25   $67.20  
  Purchase #5 $39.29   8.485%   $42.6238   $42.62   $42.60   $42.60  
  Purchase #6 $226.31   7.457%   $243.1859   $243.19   $243.20   $243.20  
  Purchase #7 $210.86   12.262%   $236.7157   $236.72   $236.70   $236.70  
  7 purchase totals = $1,097.91       $1,201.5077   $1,201.51   $1,201.50   $1,201.40