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 $92.50   5.578%   $97.6597   $97.66   $97.65   $97.70  
  Purchase #2 $45.31   6.645%   $48.3208   $48.32   $48.30   $48.30  
  Purchase #3 $11.46   7.177%   $12.2825   $12.28   $12.30   $12.30  
  Purchase #4 $167.45   7.530%   $180.059   $180.06   $180.05   $180.10  
  Purchase #5 $182.83   13.122%   $206.821   $206.82   $206.80   $206.80  
  Purchase #6 $175.79   12.122%   $197.0993   $197.10   $197.10   $197.10  
  Purchase #7 $54.99   11.448%   $61.2853   $61.29   $61.30   $61.30  
  7 purchase totals = $730.33       $803.5276   $803.53   $803.50   $803.60