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 $178.35   9.124%   $194.6227   $194.62   $194.60   $194.60  
  Purchase #2 $250.39   7.562%   $269.3245   $269.32   $269.30   $269.30  
  Purchase #3 $98.94   12.588%   $111.3946   $111.39   $111.40   $111.40  
  Purchase #4 $163.26   3.631%   $169.188   $169.19   $169.20   $169.20  
  Purchase #5 $190.44   8.858%   $207.3092   $207.31   $207.30   $207.30  
  Purchase #6 $153.75   12.506%   $172.978   $172.98   $173.00   $173.00  
  Purchase #7 $201.92   8.532%   $219.1478   $219.15   $219.15   $219.10  
  7 purchase totals = $1,237.05       $1,343.9648   $1,343.96   $1,343.95   $1,343.90