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 $64.93   12.591%   $73.1053   $73.11   $73.10   $73.10  
  Purchase #2 $181.49   13.725%   $206.3995   $206.40   $206.40   $206.40  
  Purchase #3 $247.90   9.735%   $272.0331   $272.03   $272.05   $272.00  
  Purchase #4 $235.64   3.411%   $243.6777   $243.68   $243.70   $243.70  
  Purchase #5 $204.53   12.540%   $230.1781   $230.18   $230.20   $230.20  
  Purchase #6 $77.92   10.330%   $85.9691   $85.97   $85.95   $86.00  
  Purchase #7 $43.60   3.681%   $45.2049   $45.20   $45.20   $45.20  
  7 purchase totals = $1,056.01       $1,156.5677   $1,156.57   $1,156.60   $1,156.60