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 $144.73   4.482%   $151.2168   $151.22   $151.20   $151.20  
  Purchase #2 $174.38   11.734%   $194.8417   $194.84   $194.85   $194.80  
  Purchase #3 $65.94   13.739%   $74.9995   $75.00   $75.00   $75.00  
  Purchase #4 $64.36   4.652%   $67.354   $67.35   $67.35   $67.40  
  Purchase #5 $46.85   13.700%   $53.2685   $53.27   $53.25   $53.30  
  Purchase #6 $38.47   6.700%   $41.0475   $41.05   $41.05   $41.00  
  Purchase #7 $135.59   12.278%   $152.2377   $152.24   $152.25   $152.20  
  7 purchase totals = $670.32       $734.9657   $734.97   $734.95   $734.90