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 $148.28   12.852%   $167.3369   $167.34   $167.35   $167.30  
  Purchase #2 $220.98   10.543%   $244.2779   $244.28   $244.30   $244.30  
  Purchase #3 $120.96   13.355%   $137.1142   $137.11   $137.10   $137.10  
  Purchase #4 $250.55   6.291%   $266.3121   $266.31   $266.30   $266.30  
  Purchase #5 $237.76   6.785%   $253.892   $253.89   $253.90   $253.90  
  Purchase #6 $232.95   4.783%   $244.092   $244.09   $244.10   $244.10  
  Purchase #7 $80.31   11.114%   $89.2357   $89.24   $89.25   $89.20  
  7 purchase totals = $1,291.79       $1,402.2608   $1,402.26   $1,402.30   $1,402.20