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 $202.82   12.446%   $228.063   $228.06   $228.05   $228.10  
  Purchase #2 $112.84   4.340%   $117.7373   $117.74   $117.75   $117.70  
  Purchase #3 $110.97   12.341%   $124.6648   $124.66   $124.65   $124.70  
  Purchase #4 $104.43   4.627%   $109.262   $109.26   $109.25   $109.30  
  Purchase #5 $53.30   4.207%   $55.5423   $55.54   $55.55   $55.50  
  Purchase #6 $220.78   11.821%   $246.8784   $246.88   $246.90   $246.90  
  Purchase #7 $188.99   6.607%   $201.4766   $201.48   $201.50   $201.50  
  7 purchase totals = $994.13       $1,083.6244   $1,083.62   $1,083.65   $1,083.70