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 $167.59   8.283%   $181.4715   $181.47   $181.45   $181.50  
  Purchase #2 $201.29   8.561%   $218.5224   $218.52   $218.50   $218.50  
  Purchase #3 $181.79   8.358%   $196.984   $196.98   $197.00   $197.00  
  Purchase #4 $108.69   12.708%   $122.5023   $122.50   $122.50   $122.50  
  Purchase #5 $149.66   3.225%   $154.4865   $154.49   $154.50   $154.50  
  Purchase #6 $193.86   12.203%   $217.5167   $217.52   $217.50   $217.50  
  Purchase #7 $101.46   5.208%   $106.744   $106.74   $106.75   $106.70  
  7 purchase totals = $1,104.34       $1,198.2274   $1,198.22   $1,198.20   $1,198.20