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 $58.56   11.416%   $65.2452   $65.25   $65.25   $65.20  
  Purchase #2 $170.79   7.599%   $183.7683   $183.77   $183.75   $183.80  
  Purchase #3 $166.94   13.173%   $188.931   $188.93   $188.95   $188.90  
  Purchase #4 $9.65   6.613%   $10.2882   $10.29   $10.30   $10.30  
  Purchase #5 $204.28   7.572%   $219.7481   $219.75   $219.75   $219.70  
  Purchase #6 $231.36   8.669%   $251.4166   $251.42   $251.40   $251.40  
  Purchase #7 $147.76   9.677%   $162.0587   $162.06   $162.05   $162.10  
  7 purchase totals = $989.34       $1,081.4561   $1,081.47   $1,081.45   $1,081.40