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 $114.42   10.277%   $126.1789   $126.18   $126.20   $126.20  
  Purchase #2 $181.89   11.477%   $202.7655   $202.77   $202.75   $202.80  
  Purchase #3 $41.54   7.173%   $44.5197   $44.52   $44.50   $44.50  
  Purchase #4 $233.89   10.229%   $257.8146   $257.81   $257.80   $257.80  
  Purchase #5 $195.35   12.480%   $219.7297   $219.73   $219.75   $219.70  
  Purchase #6 $66.64   11.337%   $74.195   $74.20   $74.20   $74.20  
  Purchase #7 $13.36   7.313%   $14.337   $14.34   $14.35   $14.30  
  7 purchase totals = $847.09       $939.5404   $939.55   $939.55   $939.50