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 $50.42   4.424%   $52.6506   $52.65   $52.65   $52.70  
  Purchase #2 $117.76   6.870%   $125.8501   $125.85   $125.85   $125.90  
  Purchase #3 $60.39   4.697%   $63.2265   $63.23   $63.25   $63.20  
  Purchase #4 $194.74   9.745%   $213.7174   $213.72   $213.70   $213.70  
  Purchase #5 $118.89   5.866%   $125.8641   $125.86   $125.85   $125.90  
  Purchase #6 $206.52   6.249%   $219.4254   $219.43   $219.45   $219.40  
  Purchase #7 $84.50   9.280%   $92.3416   $92.34   $92.35   $92.30  
  7 purchase totals = $833.22       $893.0757   $893.08   $893.10   $893.10