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 $83.86   5.546%   $88.5109   $88.51   $88.50   $88.50  
  Purchase #2 $11.27   10.772%   $12.484   $12.48   $12.50   $12.50  
  Purchase #3 $89.73   5.481%   $94.6481   $94.65   $94.65   $94.60  
  Purchase #4 $148.78   9.412%   $162.7832   $162.78   $162.80   $162.80  
  Purchase #5 $153.56   13.268%   $173.9343   $173.93   $173.95   $173.90  
  Purchase #6 $187.77   12.563%   $211.3595   $211.36   $211.35   $211.40  
  Purchase #7 $245.98   10.154%   $270.9568   $270.96   $270.95   $271.00  
  7 purchase totals = $920.95       $1,014.6768   $1,014.67   $1,014.70   $1,014.70