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 $247.92   13.754%   $282.0189   $282.02   $282.00   $282.00  
  Purchase #2 $171.40   6.455%   $182.4639   $182.46   $182.45   $182.50  
  Purchase #3 $150.95   6.550%   $160.8372   $160.84   $160.85   $160.80  
  Purchase #4 $230.91   4.513%   $241.331   $241.33   $241.35   $241.30  
  Purchase #5 $226.77   13.543%   $257.4815   $257.48   $257.50   $257.50  
  Purchase #6 $169.70   5.759%   $179.473   $179.47   $179.45   $179.50  
  Purchase #7 $66.64   8.668%   $72.4164   $72.42   $72.40   $72.40  
  7 purchase totals = $1,264.29       $1,376.0219   $1,376.02   $1,376.00   $1,376.00