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 $106.47   5.757%   $112.5995   $112.60   $112.60   $112.60  
  Purchase #2 $202.99   4.194%   $211.5034   $211.50   $211.50   $211.50  
  Purchase #3 $22.49   5.363%   $23.6961   $23.70   $23.70   $23.70  
  Purchase #4 $150.50   3.680%   $156.0384   $156.04   $156.05   $156.00  
  Purchase #5 $88.95   4.745%   $93.1707   $93.17   $93.15   $93.20  
  Purchase #6 $149.80   3.764%   $155.4385   $155.44   $155.45   $155.40  
  Purchase #7 $223.50   8.308%   $242.0684   $242.07   $242.05   $242.10  
  7 purchase totals = $944.70       $994.5150   $994.52   $994.50   $994.50