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 $223.58   9.572%   $244.9811   $244.98   $245.00   $245.00  
  Purchase #2 $85.70   10.543%   $94.7354   $94.74   $94.75   $94.70  
  Purchase #3 $148.69   13.632%   $168.9594   $168.96   $168.95   $169.00  
  Purchase #4 $94.73   8.817%   $103.0823   $103.08   $103.10   $103.10  
  Purchase #5 $50.73   7.686%   $54.6291   $54.63   $54.65   $54.60  
  Purchase #6 $169.91   11.822%   $189.9968   $190.00   $190.00   $190.00  
  Purchase #7 $179.30   8.828%   $195.1286   $195.13   $195.15   $195.10  
  7 purchase totals = $952.64       $1,051.5127   $1,051.52   $1,051.60   $1,051.50