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 $63.94   5.647%   $67.5507   $67.55   $67.55   $67.60  
  Purchase #2 $224.34   13.629%   $254.9153   $254.92   $254.90   $254.90  
  Purchase #3 $83.64   5.189%   $87.9801   $87.98   $88.00   $88.00  
  Purchase #4 $184.76   10.844%   $204.7954   $204.80   $204.80   $204.80  
  Purchase #5 $242.25   3.647%   $251.0849   $251.08   $251.10   $251.10  
  Purchase #6 $81.56   8.185%   $88.2357   $88.24   $88.25   $88.20  
  Purchase #7 $163.44   3.543%   $169.2307   $169.23   $169.25   $169.20  
  7 purchase totals = $1,043.93       $1,123.7928   $1,123.80   $1,123.85   $1,123.80