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 $135.78   10.289%   $149.7504   $149.75   $149.75   $149.80  
  Purchase #2 $127.25   4.806%   $133.3656   $133.37   $133.35   $133.40  
  Purchase #3 $194.52   5.128%   $204.495   $204.50   $204.50   $204.50  
  Purchase #4 $57.43   7.124%   $61.5213   $61.52   $61.50   $61.50  
  Purchase #5 $117.80   12.505%   $132.5309   $132.53   $132.55   $132.50  
  Purchase #6 $198.67   11.123%   $220.7681   $220.77   $220.75   $220.80  
  Purchase #7 $152.40   9.150%   $166.3446   $166.34   $166.35   $166.30  
  7 purchase totals = $983.85       $1,068.7759   $1,068.78   $1,068.75   $1,068.80