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 $235.32   11.375%   $262.0877   $262.09   $262.10   $262.10  
  Purchase #2 $189.55   4.127%   $197.3727   $197.37   $197.35   $197.40  
  Purchase #3 $41.29   5.800%   $43.6848   $43.68   $43.70   $43.70  
  Purchase #4 $102.26   6.468%   $108.8742   $108.87   $108.85   $108.90  
  Purchase #5 $24.36   9.236%   $26.6099   $26.61   $26.60   $26.60  
  Purchase #6 $25.49   3.145%   $26.2917   $26.29   $26.30   $26.30  
  Purchase #7 $204.79   10.465%   $226.2213   $226.22   $226.20   $226.20  
  7 purchase totals = $823.06       $891.1423   $891.13   $891.10   $891.20