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 $219.92   10.141%   $242.2221   $242.22   $242.20   $242.20  
  Purchase #2 $96.95   12.119%   $108.6994   $108.70   $108.70   $108.70  
  Purchase #3 $8.89   5.567%   $9.3849   $9.38   $9.40   $9.40  
  Purchase #4 $48.50   4.672%   $50.7659   $50.77   $50.75   $50.80  
  Purchase #5 $221.39   10.149%   $243.8589   $243.86   $243.85   $243.90  
  Purchase #6 $145.85   5.293%   $153.5698   $153.57   $153.55   $153.60  
  Purchase #7 $194.74   11.808%   $217.7349   $217.73   $217.75   $217.70  
  7 purchase totals = $936.24       $1,026.2359   $1,026.23   $1,026.20   $1,026.30