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 $202.45   12.423%   $227.6004   $227.60   $227.60   $227.60  
  Purchase #2 $194.30   6.413%   $206.7605   $206.76   $206.75   $206.80  
  Purchase #3 $102.99   7.774%   $110.9964   $111.00   $111.00   $111.00  
  Purchase #4 $119.44   12.226%   $134.0427   $134.04   $134.05   $134.00  
  Purchase #5 $236.48   3.734%   $245.3102   $245.31   $245.30   $245.30  
  Purchase #6 $5.25   10.453%   $5.7988   $5.80   $5.80   $5.80  
  Purchase #7 $33.65   9.148%   $36.7283   $36.73   $36.75   $36.70  
  7 purchase totals = $894.56       $967.2373   $967.24   $967.25   $967.20