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 $97.51   7.617%   $104.9373   $104.94   $104.95   $104.90  
  Purchase #2 $11.43   11.218%   $12.7122   $12.71   $12.70   $12.70  
  Purchase #3 $57.30   9.191%   $62.5664   $62.57   $62.55   $62.60  
  Purchase #4 $161.63   3.667%   $167.557   $167.56   $167.55   $167.60  
  Purchase #5 $217.82   3.687%   $225.851   $225.85   $225.85   $225.90  
  Purchase #6 $128.65   5.816%   $136.1323   $136.13   $136.15   $136.10  
  Purchase #7 $57.85   5.162%   $60.8362   $60.84   $60.85   $60.80  
  7 purchase totals = $732.19       $770.5924   $770.60   $770.60   $770.60