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 $92.99   11.449%   $103.6364   $103.64   $103.65   $103.60  
  Purchase #2 $221.94   12.551%   $249.7957   $249.80   $249.80   $249.80  
  Purchase #3 $38.27   3.371%   $39.5601   $39.56   $39.55   $39.60  
  Purchase #4 $201.37   11.446%   $224.4188   $224.42   $224.40   $224.40  
  Purchase #5 $85.68   11.665%   $95.6746   $95.67   $95.65   $95.70  
  Purchase #6 $94.58   8.738%   $102.8444   $102.84   $102.85   $102.80  
  Purchase #7 $224.55   8.668%   $244.014   $244.01   $244.00   $244.00  
  7 purchase totals = $959.38       $1,059.9440   $1,059.94   $1,059.90   $1,059.90