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 $194.87   13.356%   $220.8968   $220.90   $220.90   $220.90  
  Purchase #2 $195.43   13.190%   $221.2072   $221.21   $221.20   $221.20  
  Purchase #3 $27.69   12.518%   $31.1562   $31.16   $31.15   $31.20  
  Purchase #4 $27.73   13.107%   $31.3646   $31.36   $31.35   $31.40  
  Purchase #5 $218.87   4.546%   $228.8198   $228.82   $228.80   $228.80  
  Purchase #6 $34.33   10.849%   $38.0545   $38.05   $38.05   $38.10  
  Purchase #7 $63.32   13.433%   $71.8258   $71.83   $71.85   $71.80  
  7 purchase totals = $762.24       $843.3249   $843.33   $843.30   $843.40