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 $82.36   12.102%   $92.3272   $92.33   $92.35   $92.30  
  Purchase #2 $202.50   11.456%   $225.6984   $225.70   $225.70   $225.70  
  Purchase #3 $238.42   6.689%   $254.3679   $254.37   $254.35   $254.40  
  Purchase #4 $94.65   8.209%   $102.4198   $102.42   $102.40   $102.40  
  Purchase #5 $189.31   10.749%   $209.6589   $209.66   $209.65   $209.70  
  Purchase #6 $23.69   11.759%   $26.4757   $26.48   $26.50   $26.50  
  Purchase #7 $54.41   8.640%   $59.111   $59.11   $59.10   $59.10  
  7 purchase totals = $885.34       $970.0589   $970.07   $970.05   $970.10