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 $196.32   4.280%   $204.7225   $204.72   $204.70   $204.70  
  Purchase #2 $20.78   6.243%   $22.0773   $22.08   $22.10   $22.10  
  Purchase #3 $93.45   8.413%   $101.3119   $101.31   $101.30   $101.30  
  Purchase #4 $70.27   7.520%   $75.5543   $75.55   $75.55   $75.60  
  Purchase #5 $68.52   3.868%   $71.1704   $71.17   $71.15   $71.20  
  Purchase #6 $94.68   9.649%   $103.8157   $103.82   $103.80   $103.80  
  Purchase #7 $233.73   6.130%   $248.0576   $248.06   $248.05   $248.10  
  7 purchase totals = $777.75       $826.7097   $826.71   $826.65   $826.80