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 $84.76   9.746%   $93.0207   $93.02   $93.00   $93.00  
  Purchase #2 $198.26   5.731%   $209.6223   $209.62   $209.60   $209.60  
  Purchase #3 $212.32   8.810%   $231.0254   $231.03   $231.05   $231.00  
  Purchase #4 $162.77   13.551%   $184.827   $184.83   $184.85   $184.80  
  Purchase #5 $62.74   13.699%   $71.3348   $71.33   $71.35   $71.30  
  Purchase #6 $225.41   11.412%   $251.1338   $251.13   $251.15   $251.10  
  Purchase #7 $196.25   3.485%   $203.0893   $203.09   $203.10   $203.10  
  7 purchase totals = $1,142.51       $1,244.0533   $1,244.05   $1,244.10   $1,243.90