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 $152.67   6.278%   $162.2546   $162.25   $162.25   $162.30  
  Purchase #2 $107.98   5.780%   $114.2212   $114.22   $114.20   $114.20  
  Purchase #3 $245.30   5.758%   $259.4244   $259.42   $259.40   $259.40  
  Purchase #4 $211.90   9.224%   $231.4457   $231.45   $231.45   $231.40  
  Purchase #5 $87.35   5.528%   $92.1787   $92.18   $92.20   $92.20  
  Purchase #6 $94.80   11.818%   $106.0035   $106.00   $106.00   $106.00  
  Purchase #7 $63.52   5.831%   $67.2239   $67.22   $67.20   $67.20  
  7 purchase totals = $963.52       $1,032.7520   $1,032.74   $1,032.70   $1,032.70