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 $118.40   12.197%   $132.8412   $132.84   $132.85   $132.80  
  Purchase #2 $98.56   12.241%   $110.6247   $110.62   $110.60   $110.60  
  Purchase #3 $146.33   11.389%   $162.9955   $163.00   $163.00   $163.00  
  Purchase #4 $205.93   9.572%   $225.6416   $225.64   $225.65   $225.60  
  Purchase #5 $147.90   6.334%   $157.268   $157.27   $157.25   $157.30  
  Purchase #6 $162.51   10.411%   $179.4289   $179.43   $179.45   $179.40  
  Purchase #7 $52.56   7.122%   $56.3033   $56.30   $56.30   $56.30  
  7 purchase totals = $932.19       $1,025.1032   $1,025.10   $1,025.10   $1,025.00