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 $117.62   6.407%   $125.1559   $125.16   $125.15   $125.20  
  Purchase #2 $103.43   4.138%   $107.7099   $107.71   $107.70   $107.70  
  Purchase #3 $194.56   13.561%   $220.9443   $220.94   $220.95   $220.90  
  Purchase #4 $201.84   9.798%   $221.6163   $221.62   $221.60   $221.60  
  Purchase #5 $181.90   7.159%   $194.9222   $194.92   $194.90   $194.90  
  Purchase #6 $12.63   8.810%   $13.7427   $13.74   $13.75   $13.70  
  Purchase #7 $145.93   13.743%   $165.9852   $165.99   $166.00   $166.00  
  7 purchase totals = $957.91       $1,050.0765   $1,050.08   $1,050.05   $1,050.00