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 $232.57   5.348%   $245.0078   $245.01   $245.00   $245.00  
  Purchase #2 $179.97   9.483%   $197.0366   $197.04   $197.05   $197.00  
  Purchase #3 $56.43   10.503%   $62.3568   $62.36   $62.35   $62.40  
  Purchase #4 $128.71   11.583%   $143.6185   $143.62   $143.60   $143.60  
  Purchase #5 $148.70   9.807%   $163.283   $163.28   $163.30   $163.30  
  Purchase #6 $166.51   7.616%   $179.1914   $179.19   $179.20   $179.20  
  Purchase #7 $86.98   6.469%   $92.6067   $92.61   $92.60   $92.60  
  7 purchase totals = $999.87       $1,083.1008   $1,083.11   $1,083.10   $1,083.10