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 $110.52   9.388%   $120.8956   $120.90   $120.90   $120.90  
  Purchase #2 $78.56   5.410%   $82.8101   $82.81   $82.80   $82.80  
  Purchase #3 $94.69   13.595%   $107.5631   $107.56   $107.55   $107.60  
  Purchase #4 $231.92   9.374%   $253.6602   $253.66   $253.65   $253.70  
  Purchase #5 $124.71   4.478%   $130.2945   $130.29   $130.30   $130.30  
  Purchase #6 $120.68   7.682%   $129.9506   $129.95   $129.95   $130.00  
  Purchase #7 $41.77   3.143%   $43.0828   $43.08   $43.10   $43.10  
  7 purchase totals = $802.85       $868.2569   $868.25   $868.25   $868.40