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 $205.73   9.122%   $224.4967   $224.50   $224.50   $224.50  
  Purchase #2 $248.35   11.433%   $276.7439   $276.74   $276.75   $276.70  
  Purchase #3 $150.27   10.399%   $165.8966   $165.90   $165.90   $165.90  
  Purchase #4 $76.86   11.329%   $85.5675   $85.57   $85.55   $85.60  
  Purchase #5 $145.52   11.327%   $162.0031   $162.00   $162.00   $162.00  
  Purchase #6 $89.42   8.654%   $97.1584   $97.16   $97.15   $97.20  
  Purchase #7 $249.26   6.196%   $264.7041   $264.70   $264.70   $264.70  
  7 purchase totals = $1,165.41       $1,276.5703   $1,276.57   $1,276.55   $1,276.60