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 $184.58   8.709%   $200.6551   $200.66   $200.65   $200.70  
  Purchase #2 $135.83   3.695%   $140.8489   $140.85   $140.85   $140.80  
  Purchase #3 $219.93   4.826%   $230.5438   $230.54   $230.55   $230.50  
  Purchase #4 $89.27   5.515%   $94.1932   $94.19   $94.20   $94.20  
  Purchase #5 $88.78   12.408%   $99.7958   $99.80   $99.80   $99.80  
  Purchase #6 $25.39   10.589%   $28.0785   $28.08   $28.10   $28.10  
  Purchase #7 $137.66   9.632%   $150.9194   $150.92   $150.90   $150.90  
  7 purchase totals = $881.44       $945.0347   $945.04   $945.05   $945.00