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 $22.47   9.416%   $24.5858   $24.59   $24.60   $24.60  
  Purchase #2 $231.91   6.543%   $247.0839   $247.08   $247.10   $247.10  
  Purchase #3 $18.52   10.855%   $20.5303   $20.53   $20.55   $20.50  
  Purchase #4 $67.62   13.683%   $76.8724   $76.87   $76.85   $76.90  
  Purchase #5 $65.61   9.695%   $71.9709   $71.97   $71.95   $72.00  
  Purchase #6 $189.69   3.771%   $196.8432   $196.84   $196.85   $196.80  
  Purchase #7 $242.31   5.731%   $256.1968   $256.20   $256.20   $256.20  
  7 purchase totals = $838.13       $894.0833   $894.08   $894.10   $894.10