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 $246.39   9.301%   $269.3067   $269.31   $269.30   $269.30  
  Purchase #2 $220.28   12.285%   $247.3414   $247.34   $247.35   $247.30  
  Purchase #3 $197.81   12.553%   $222.6411   $222.64   $222.65   $222.60  
  Purchase #4 $62.92   6.761%   $67.174   $67.17   $67.15   $67.20  
  Purchase #5 $230.81   10.339%   $254.6734   $254.67   $254.65   $254.70  
  Purchase #6 $142.98   10.155%   $157.4996   $157.50   $157.50   $157.50  
  Purchase #7 $101.51   4.459%   $106.0363   $106.04   $106.05   $106.00  
  7 purchase totals = $1,202.70       $1,324.6725   $1,324.67   $1,324.65   $1,324.60