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 $245.29   8.734%   $266.7136   $266.71   $266.70   $266.70  
  Purchase #2 $218.53   13.212%   $247.4022   $247.40   $247.40   $247.40  
  Purchase #3 $44.38   9.140%   $48.4363   $48.44   $48.45   $48.40  
  Purchase #4 $181.42   9.586%   $198.8109   $198.81   $198.80   $198.80  
  Purchase #5 $97.91   4.732%   $102.5431   $102.54   $102.55   $102.50  
  Purchase #6 $235.43   7.549%   $253.2026   $253.20   $253.20   $253.20  
  Purchase #7 $216.71   12.584%   $243.9808   $243.98   $244.00   $244.00  
  7 purchase totals = $1,239.67       $1,361.0895   $1,361.08   $1,361.10   $1,361.00