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 $216.62   11.418%   $241.3537   $241.35   $241.35   $241.40  
  Purchase #2 $198.25   8.787%   $215.6702   $215.67   $215.65   $215.70  
  Purchase #3 $215.85   13.418%   $244.8128   $244.81   $244.80   $244.80  
  Purchase #4 $63.82   8.818%   $69.4476   $69.45   $69.45   $69.40  
  Purchase #5 $211.50   12.367%   $237.6562   $237.66   $237.65   $237.70  
  Purchase #6 $128.44   3.143%   $132.4769   $132.48   $132.50   $132.50  
  Purchase #7 $95.52   4.237%   $99.5672   $99.57   $99.55   $99.60  
  7 purchase totals = $1,130.00       $1,240.9846   $1,240.99   $1,240.95   $1,241.10