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 $93.47   13.386%   $105.9819   $105.98   $106.00   $106.00  
  Purchase #2 $162.72   6.719%   $173.6532   $173.65   $173.65   $173.70  
  Purchase #3 $64.30   3.383%   $66.4753   $66.48   $66.50   $66.50  
  Purchase #4 $69.59   7.467%   $74.7863   $74.79   $74.80   $74.80  
  Purchase #5 $93.52   9.322%   $102.2379   $102.24   $102.25   $102.20  
  Purchase #6 $202.52   7.769%   $218.2538   $218.25   $218.25   $218.30  
  Purchase #7 $97.40   10.363%   $107.4936   $107.49   $107.50   $107.50  
  7 purchase totals = $783.52       $848.8820   $848.88   $848.95   $849.00