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 $63.26   11.357%   $70.4444   $70.44   $70.45   $70.40  
  Purchase #2 $250.32   6.799%   $267.3393   $267.34   $267.35   $267.30  
  Purchase #3 $50.38   6.202%   $53.5046   $53.50   $53.50   $53.50  
  Purchase #4 $147.84   3.415%   $152.8887   $152.89   $152.90   $152.90  
  Purchase #5 $155.97   9.557%   $170.8761   $170.88   $170.90   $170.90  
  Purchase #6 $196.97   12.139%   $220.8802   $220.88   $220.90   $220.90  
  Purchase #7 $44.37   12.745%   $50.025   $50.03   $50.05   $50.00  
  7 purchase totals = $909.11       $985.9583   $985.96   $986.05   $985.90