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 $241.52   10.559%   $267.0221   $267.02   $267.00   $267.00  
  Purchase #2 $165.25   3.811%   $171.5477   $171.55   $171.55   $171.50  
  Purchase #3 $173.99   5.758%   $184.0083   $184.01   $184.00   $184.00  
  Purchase #4 $85.89   8.211%   $92.9424   $92.94   $92.95   $92.90  
  Purchase #5 $5.39   7.753%   $5.8079   $5.81   $5.80   $5.80  
  Purchase #6 $66.89   8.478%   $72.5609   $72.56   $72.55   $72.60  
  Purchase #7 $238.34   4.596%   $249.2941   $249.29   $249.30   $249.30  
  7 purchase totals = $977.27       $1,043.1834   $1,043.18   $1,043.15   $1,043.10