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 $58.65   12.874%   $66.2006   $66.20   $66.20   $66.20  
  Purchase #2 $210.42   12.363%   $236.4342   $236.43   $236.45   $236.40  
  Purchase #3 $240.96   3.685%   $249.8394   $249.84   $249.85   $249.80  
  Purchase #4 $168.59   3.759%   $174.9273   $174.93   $174.95   $174.90  
  Purchase #5 $166.78   3.597%   $172.7791   $172.78   $172.80   $172.80  
  Purchase #6 $100.40   5.579%   $106.0013   $106.00   $106.00   $106.00  
  Purchase #7 $127.36   6.568%   $135.725   $135.73   $135.75   $135.70  
  7 purchase totals = $1,073.16       $1,141.9069   $1,141.91   $1,142.00   $1,141.80