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 $52.34   11.263%   $58.2351   $58.24   $58.25   $58.20  
  Purchase #2 $109.68   10.612%   $121.3192   $121.32   $121.30   $121.30  
  Purchase #3 $167.37   5.156%   $175.9996   $176.00   $176.00   $176.00  
  Purchase #4 $113.37   12.363%   $127.3859   $127.39   $127.40   $127.40  
  Purchase #5 $179.91   12.192%   $201.8446   $201.84   $201.85   $201.80  
  Purchase #6 $113.59   11.829%   $127.0266   $127.03   $127.05   $127.00  
  Purchase #7 $124.48   12.735%   $140.3325   $140.33   $140.35   $140.30  
  7 purchase totals = $860.74       $952.1435   $952.15   $952.20   $952.00