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 $93.25   6.245%   $99.0735   $99.07   $99.05   $99.10  
  Purchase #2 $187.32   8.719%   $203.6524   $203.65   $203.65   $203.70  
  Purchase #3 $41.96   6.134%   $44.5338   $44.53   $44.55   $44.50  
  Purchase #4 $67.97   4.394%   $70.9566   $70.96   $70.95   $71.00  
  Purchase #5 $215.32   7.168%   $230.7541   $230.75   $230.75   $230.80  
  Purchase #6 $165.30   5.845%   $174.9618   $174.96   $174.95   $175.00  
  Purchase #7 $150.97   3.504%   $156.26   $156.26   $156.25   $156.30  
  7 purchase totals = $922.09       $980.1922   $980.18   $980.15   $980.40