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 $64.28   4.158%   $66.9528   $66.95   $66.95   $67.00  
  Purchase #2 $220.81   7.613%   $237.6203   $237.62   $237.60   $237.60  
  Purchase #3 $249.70   11.143%   $277.5241   $277.52   $277.50   $277.50  
  Purchase #4 $247.25   8.421%   $268.0709   $268.07   $268.05   $268.10  
  Purchase #5 $215.46   10.624%   $238.3505   $238.35   $238.35   $238.40  
  Purchase #6 $225.39   7.200%   $241.6181   $241.62   $241.60   $241.60  
  Purchase #7 $63.70   5.294%   $67.0723   $67.07   $67.05   $67.10  
  7 purchase totals = $1,286.59       $1,397.2090   $1,397.20   $1,397.10   $1,397.30