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 $197.92   3.246%   $204.3445   $204.34   $204.35   $204.30  
  Purchase #2 $126.46   13.615%   $143.6775   $143.68   $143.70   $143.70  
  Purchase #3 $244.85   6.454%   $260.6526   $260.65   $260.65   $260.70  
  Purchase #4 $236.88   9.520%   $259.431   $259.43   $259.45   $259.40  
  Purchase #5 $26.46   12.187%   $29.6847   $29.68   $29.70   $29.70  
  Purchase #6 $130.92   13.552%   $148.6623   $148.66   $148.65   $148.70  
  Purchase #7 $128.41   9.195%   $140.2173   $140.22   $140.20   $140.20  
  7 purchase totals = $1,091.90       $1,186.6699   $1,186.66   $1,186.70   $1,186.70