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 $67.74   13.114%   $76.6234   $76.62   $76.60   $76.60  
  Purchase #2 $187.75   8.234%   $203.2093   $203.21   $203.20   $203.20  
  Purchase #3 $22.26   9.162%   $24.2995   $24.30   $24.30   $24.30  
  Purchase #4 $223.72   8.472%   $242.6736   $242.67   $242.65   $242.70  
  Purchase #5 $205.26   7.598%   $220.8557   $220.86   $220.85   $220.90  
  Purchase #6 $127.62   10.674%   $141.2422   $141.24   $141.25   $141.20  
  Purchase #7 $216.82   9.167%   $236.6959   $236.70   $236.70   $236.70  
  7 purchase totals = $1,051.17       $1,145.5996   $1,145.60   $1,145.55   $1,145.60