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 $179.91   11.788%   $201.1178   $201.12   $201.10   $201.10  
  Purchase #2 $25.82   3.599%   $26.7493   $26.75   $26.75   $26.70  
  Purchase #3 $163.55   6.363%   $173.9567   $173.96   $173.95   $174.00  
  Purchase #4 $55.88   12.503%   $62.8667   $62.87   $62.85   $62.90  
  Purchase #5 $156.38   11.386%   $174.1854   $174.19   $174.20   $174.20  
  Purchase #6 $216.87   4.187%   $225.9503   $225.95   $225.95   $226.00  
  Purchase #7 $225.55   3.456%   $233.345   $233.35   $233.35   $233.30  
  7 purchase totals = $1,023.96       $1,098.1712   $1,098.19   $1,098.15   $1,098.20