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 $126.68   11.530%   $141.2862   $141.29   $141.30   $141.30  
  Purchase #2 $199.46   5.425%   $210.2807   $210.28   $210.30   $210.30  
  Purchase #3 $136.96   3.330%   $141.5208   $141.52   $141.50   $141.50  
  Purchase #4 $250.50   5.384%   $263.9869   $263.99   $264.00   $264.00  
  Purchase #5 $206.44   7.841%   $222.627   $222.63   $222.65   $222.60  
  Purchase #6 $181.93   5.690%   $192.2818   $192.28   $192.30   $192.30  
  Purchase #7 $64.68   6.702%   $69.0149   $69.01   $69.00   $69.00  
  7 purchase totals = $1,166.65       $1,240.9983   $1,241.00   $1,241.05   $1,241.00