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 $96.69   4.821%   $101.3514   $101.35   $101.35   $101.40  
  Purchase #2 $54.74   11.482%   $61.0252   $61.03   $61.05   $61.00  
  Purchase #3 $120.32   5.127%   $126.4888   $126.49   $126.50   $126.50  
  Purchase #4 $78.59   11.133%   $87.3394   $87.34   $87.35   $87.30  
  Purchase #5 $200.84   7.417%   $215.7363   $215.74   $215.75   $215.70  
  Purchase #6 $54.98   3.708%   $57.0187   $57.02   $57.00   $57.00  
  Purchase #7 $135.44   11.762%   $151.3705   $151.37   $151.35   $151.40  
  7 purchase totals = $741.60       $800.3303   $800.34   $800.35   $800.30