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 $222.94   13.114%   $252.1764   $252.18   $252.20   $252.20  
  Purchase #2 $66.82   5.457%   $70.4664   $70.47   $70.45   $70.50  
  Purchase #3 $238.98   12.713%   $269.3615   $269.36   $269.35   $269.40  
  Purchase #4 $45.41   6.599%   $48.4066   $48.41   $48.40   $48.40  
  Purchase #5 $57.62   11.690%   $64.3558   $64.36   $64.35   $64.40  
  Purchase #6 $124.70   7.428%   $133.9627   $133.96   $133.95   $134.00  
  Purchase #7 $171.64   12.637%   $193.3301   $193.33   $193.35   $193.30  
  7 purchase totals = $928.11       $1,032.0595   $1,032.07   $1,032.05   $1,032.20