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 $75.66   13.565%   $85.9233   $85.92   $85.90   $85.90  
  Purchase #2 $167.96   7.125%   $179.9272   $179.93   $179.95   $179.90  
  Purchase #3 $82.66   12.258%   $92.7925   $92.79   $92.80   $92.80  
  Purchase #4 $77.47   13.369%   $87.827   $87.83   $87.85   $87.80  
  Purchase #5 $58.75   4.564%   $61.4314   $61.43   $61.45   $61.40  
  Purchase #6 $211.88   5.862%   $224.3004   $224.30   $224.30   $224.30  
  Purchase #7 $217.67   11.144%   $241.9271   $241.93   $241.95   $241.90  
  7 purchase totals = $892.05       $974.1289   $974.13   $974.20   $974.00