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 $201.42   12.779%   $227.1595   $227.16   $227.15   $227.20  
  Purchase #2 $181.67   6.764%   $193.9582   $193.96   $193.95   $194.00  
  Purchase #3 $79.98   10.571%   $88.4347   $88.43   $88.45   $88.40  
  Purchase #4 $26.67   3.289%   $27.5472   $27.55   $27.55   $27.50  
  Purchase #5 $212.61   11.444%   $236.9411   $236.94   $236.95   $236.90  
  Purchase #6 $88.50   6.637%   $94.3737   $94.37   $94.35   $94.40  
  Purchase #7 $226.27   6.769%   $241.5862   $241.59   $241.60   $241.60  
  7 purchase totals = $1,017.12       $1,110.0006   $1,110.00   $1,110.00   $1,110.00