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 $20.86   13.320%   $23.6386   $23.64   $23.65   $23.60  
  Purchase #2 $203.77   7.572%   $219.1995   $219.20   $219.20   $219.20  
  Purchase #3 $86.42   6.438%   $91.9837   $91.98   $92.00   $92.00  
  Purchase #4 $56.75   13.268%   $64.2796   $64.28   $64.30   $64.30  
  Purchase #5 $217.85   12.434%   $244.9375   $244.94   $244.95   $244.90  
  Purchase #6 $68.59   9.418%   $75.0498   $75.05   $75.05   $75.00  
  Purchase #7 $223.85   10.737%   $247.8848   $247.88   $247.90   $247.90  
  7 purchase totals = $878.09       $966.9735   $966.97   $967.05   $966.90