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 $53.98   4.252%   $56.2752   $56.28   $56.30   $56.30  
  Purchase #2 $184.74   4.841%   $193.6833   $193.68   $193.70   $193.70  
  Purchase #3 $217.53   10.113%   $239.5288   $239.53   $239.55   $239.50  
  Purchase #4 $234.27   10.212%   $258.1937   $258.19   $258.20   $258.20  
  Purchase #5 $212.69   9.129%   $232.1065   $232.11   $232.10   $232.10  
  Purchase #6 $223.31   5.397%   $235.362   $235.36   $235.35   $235.40  
  Purchase #7 $29.28   8.847%   $31.8704   $31.87   $31.85   $31.90  
  7 purchase totals = $1,155.80       $1,247.0199   $1,247.02   $1,247.05   $1,247.10