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 $34.98   10.623%   $38.6959   $38.70   $38.70   $38.70  
  Purchase #2 $83.33   12.793%   $93.9904   $93.99   $94.00   $94.00  
  Purchase #3 $111.50   6.873%   $119.1634   $119.16   $119.15   $119.20  
  Purchase #4 $185.33   12.281%   $208.0904   $208.09   $208.10   $208.10  
  Purchase #5 $207.29   10.244%   $228.5248   $228.52   $228.50   $228.50  
  Purchase #6 $203.80   11.445%   $227.1249   $227.12   $227.10   $227.10  
  Purchase #7 $51.55   8.189%   $55.7714   $55.77   $55.75   $55.80  
  7 purchase totals = $877.78       $971.3612   $971.35   $971.30   $971.40