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 $82.73   12.325%   $92.9265   $92.93   $92.95   $92.90  
  Purchase #2 $246.55   11.594%   $275.135   $275.14   $275.15   $275.10  
  Purchase #3 $79.62   8.415%   $86.32   $86.32   $86.30   $86.30  
  Purchase #4 $243.82   8.106%   $263.584   $263.58   $263.60   $263.60  
  Purchase #5 $238.28   6.373%   $253.4656   $253.47   $253.45   $253.50  
  Purchase #6 $208.71   9.406%   $228.3413   $228.34   $228.35   $228.30  
  Purchase #7 $167.88   3.364%   $173.5275   $173.53   $173.55   $173.50  
  7 purchase totals = $1,267.59       $1,373.2999   $1,373.31   $1,373.35   $1,373.20