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 $164.61   13.597%   $186.992   $186.99   $187.00   $187.00  
  Purchase #2 $17.93   8.804%   $19.5086   $19.51   $19.50   $19.50  
  Purchase #3 $94.95   13.619%   $107.8812   $107.88   $107.90   $107.90  
  Purchase #4 $204.88   9.171%   $223.6695   $223.67   $223.65   $223.70  
  Purchase #5 $132.61   12.588%   $149.3029   $149.30   $149.30   $149.30  
  Purchase #6 $138.87   8.445%   $150.5976   $150.60   $150.60   $150.60  
  Purchase #7 $23.60   3.339%   $24.388   $24.39   $24.40   $24.40  
  7 purchase totals = $777.45       $862.3398   $862.34   $862.35   $862.40