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 $228.31   7.755%   $246.0154   $246.02   $246.00   $246.00  
  Purchase #2 $69.74   4.324%   $72.7556   $72.76   $72.75   $72.80  
  Purchase #3 $102.45   12.744%   $115.5062   $115.51   $115.50   $115.50  
  Purchase #4 $206.45   4.702%   $216.1573   $216.16   $216.15   $216.20  
  Purchase #5 $193.74   5.549%   $204.4906   $204.49   $204.50   $204.50  
  Purchase #6 $58.92   4.107%   $61.3398   $61.34   $61.35   $61.30  
  Purchase #7 $113.52   8.789%   $123.4973   $123.50   $123.50   $123.50  
  7 purchase totals = $973.13       $1,039.7622   $1,039.78   $1,039.75   $1,039.80