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 $66.96   11.678%   $74.7796   $74.78   $74.80   $74.80  
  Purchase #2 $148.29   10.102%   $163.2703   $163.27   $163.25   $163.30  
  Purchase #3 $157.51   13.199%   $178.2997   $178.30   $178.30   $178.30  
  Purchase #4 $59.34   7.867%   $64.0083   $64.01   $64.00   $64.00  
  Purchase #5 $219.72   13.210%   $248.745   $248.75   $248.75   $248.70  
  Purchase #6 $171.62   11.398%   $191.1812   $191.18   $191.20   $191.20  
  Purchase #7 $106.36   6.511%   $113.2851   $113.29   $113.30   $113.30  
  7 purchase totals = $929.80       $1,033.5692   $1,033.58   $1,033.60   $1,033.60