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 $150.68   11.522%   $168.0413   $168.04   $168.05   $168.00  
  Purchase #2 $102.93   8.751%   $111.9374   $111.94   $111.95   $111.90  
  Purchase #3 $193.45   5.237%   $203.581   $203.58   $203.60   $203.60  
  Purchase #4 $176.42   7.657%   $189.9285   $189.93   $189.95   $189.90  
  Purchase #5 $237.91   5.803%   $251.7159   $251.72   $251.70   $251.70  
  Purchase #6 $60.43   7.397%   $64.9   $64.90   $64.90   $64.90  
  Purchase #7 $171.66   9.397%   $187.7909   $187.79   $187.80   $187.80  
  7 purchase totals = $1,093.48       $1,177.8950   $1,177.90   $1,177.95   $1,177.80