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 $43.88   11.284%   $48.8314   $48.83   $48.85   $48.80  
  Purchase #2 $239.57   11.217%   $266.4426   $266.44   $266.45   $266.40  
  Purchase #3 $185.34   11.467%   $206.5929   $206.59   $206.60   $206.60  
  Purchase #4 $167.51   12.241%   $188.0149   $188.01   $188.00   $188.00  
  Purchase #5 $39.94   3.676%   $41.4082   $41.41   $41.40   $41.40  
  Purchase #6 $178.66   13.445%   $202.6808   $202.68   $202.70   $202.70  
  Purchase #7 $194.40   12.677%   $219.0441   $219.04   $219.05   $219.00  
  7 purchase totals = $1,049.30       $1,173.0149   $1,173.00   $1,173.05   $1,172.90