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 $204.82   11.606%   $228.5914   $228.59   $228.60   $228.60  
  Purchase #2 $224.62   13.134%   $254.1216   $254.12   $254.10   $254.10  
  Purchase #3 $106.63   12.799%   $120.2776   $120.28   $120.30   $120.30  
  Purchase #4 $216.97   6.776%   $231.6719   $231.67   $231.65   $231.70  
  Purchase #5 $206.60   8.492%   $224.1445   $224.14   $224.15   $224.10  
  Purchase #6 $10.94   4.351%   $11.416   $11.42   $11.40   $11.40  
  Purchase #7 $161.71   9.829%   $177.6045   $177.60   $177.60   $177.60  
  7 purchase totals = $1,132.29       $1,247.8275   $1,247.82   $1,247.80   $1,247.80