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 $194.29   12.322%   $218.2304   $218.23   $218.25   $218.20  
  Purchase #2 $58.99   9.628%   $64.6696   $64.67   $64.65   $64.70  
  Purchase #3 $88.65   8.426%   $96.1196   $96.12   $96.10   $96.10  
  Purchase #4 $189.56   6.314%   $201.5288   $201.53   $201.55   $201.50  
  Purchase #5 $233.86   5.499%   $246.72   $246.72   $246.70   $246.70  
  Purchase #6 $108.62   3.252%   $112.1523   $112.15   $112.15   $112.20  
  Purchase #7 $233.81   4.784%   $244.9955   $245.00   $245.00   $245.00  
  7 purchase totals = $1,107.78       $1,184.4162   $1,184.42   $1,184.40   $1,184.40