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 $218.41   12.468%   $245.6414   $245.64   $245.65   $245.60  
  Purchase #2 $46.39   8.219%   $50.2028   $50.20   $50.20   $50.20  
  Purchase #3 $114.46   6.573%   $121.9835   $121.98   $122.00   $122.00  
  Purchase #4 $225.34   13.221%   $255.1322   $255.13   $255.15   $255.10  
  Purchase #5 $248.74   5.513%   $262.453   $262.45   $262.45   $262.50  
  Purchase #6 $162.80   11.158%   $180.9652   $180.97   $180.95   $181.00  
  Purchase #7 $31.39   3.386%   $32.4529   $32.45   $32.45   $32.50  
  7 purchase totals = $1,047.53       $1,148.8310   $1,148.82   $1,148.85   $1,148.90