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 $48.78   13.416%   $55.3243   $55.32   $55.30   $55.30  
  Purchase #2 $153.65   6.449%   $163.5589   $163.56   $163.55   $163.60  
  Purchase #3 $97.43   6.706%   $103.9637   $103.96   $103.95   $104.00  
  Purchase #4 $194.89   4.702%   $204.0537   $204.05   $204.05   $204.10  
  Purchase #5 $97.62   13.373%   $110.6747   $110.67   $110.65   $110.70  
  Purchase #6 $181.30   9.796%   $199.0601   $199.06   $199.05   $199.10  
  Purchase #7 $21.79   9.252%   $23.806   $23.81   $23.80   $23.80  
  7 purchase totals = $795.46       $860.4414   $860.43   $860.35   $860.60