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 $118.45   3.804%   $122.9558   $122.96   $122.95   $123.00  
  Purchase #2 $56.74   13.305%   $64.2893   $64.29   $64.30   $64.30  
  Purchase #3 $188.60   5.455%   $198.8881   $198.89   $198.90   $198.90  
  Purchase #4 $101.33   4.724%   $106.1168   $106.12   $106.10   $106.10  
  Purchase #5 $162.61   11.708%   $181.6484   $181.65   $181.65   $181.60  
  Purchase #6 $250.35   6.780%   $267.3237   $267.32   $267.30   $267.30  
  Purchase #7 $211.94   13.862%   $241.3191   $241.32   $241.30   $241.30  
  7 purchase totals = $1,090.02       $1,182.5412   $1,182.55   $1,182.50   $1,182.50