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 $213.80   13.648%   $242.9794   $242.98   $243.00   $243.00  
  Purchase #2 $88.81   8.662%   $96.5027   $96.50   $96.50   $96.50  
  Purchase #3 $90.44   12.253%   $101.5216   $101.52   $101.50   $101.50  
  Purchase #4 $47.85   3.768%   $49.653   $49.65   $49.65   $49.70  
  Purchase #5 $214.60   4.284%   $223.7935   $223.79   $223.80   $223.80  
  Purchase #6 $88.98   11.847%   $99.5215   $99.52   $99.50   $99.50  
  Purchase #7 $191.32   5.222%   $201.3107   $201.31   $201.30   $201.30  
  7 purchase totals = $935.80       $1,015.2824   $1,015.27   $1,015.25   $1,015.30