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 $58.47   5.580%   $61.7326   $61.73   $61.75   $61.70  
  Purchase #2 $53.73   9.573%   $58.8736   $58.87   $58.85   $58.90  
  Purchase #3 $185.56   9.294%   $202.8059   $202.81   $202.80   $202.80  
  Purchase #4 $175.42   10.639%   $194.0829   $194.08   $194.10   $194.10  
  Purchase #5 $97.42   5.737%   $103.009   $103.01   $103.00   $103.00  
  Purchase #6 $193.37   10.619%   $213.904   $213.90   $213.90   $213.90  
  Purchase #7 $176.27   5.853%   $186.5871   $186.59   $186.60   $186.60  
  7 purchase totals = $940.24       $1,020.9951   $1,020.99   $1,021.00   $1,021.00