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 $89.93   7.716%   $96.869   $96.87   $96.85   $96.90  
  Purchase #2 $172.96   5.327%   $182.1736   $182.17   $182.15   $182.20  
  Purchase #3 $121.45   10.400%   $134.0808   $134.08   $134.10   $134.10  
  Purchase #4 $53.74   8.740%   $58.4369   $58.44   $58.45   $58.40  
  Purchase #5 $194.89   5.517%   $205.6421   $205.64   $205.65   $205.60  
  Purchase #6 $5.27   13.406%   $5.9765   $5.98   $6.00   $6.00  
  Purchase #7 $118.59   4.581%   $124.0226   $124.02   $124.00   $124.00  
  7 purchase totals = $756.83       $807.2015   $807.20   $807.20   $807.20