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 $193.85   7.112%   $207.6366   $207.64   $207.65   $207.60  
  Purchase #2 $179.90   13.456%   $204.1073   $204.11   $204.10   $204.10  
  Purchase #3 $77.46   3.589%   $80.24   $80.24   $80.25   $80.20  
  Purchase #4 $90.67   13.450%   $102.8651   $102.87   $102.85   $102.90  
  Purchase #5 $148.60   13.862%   $169.1989   $169.20   $169.20   $169.20  
  Purchase #6 $54.31   12.830%   $61.278   $61.28   $61.30   $61.30  
  Purchase #7 $248.85   5.538%   $262.6313   $262.63   $262.65   $262.60  
  7 purchase totals = $993.64       $1,087.9572   $1,087.97   $1,088.00   $1,087.90