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 $184.97   9.558%   $202.6494   $202.65   $202.65   $202.60  
  Purchase #2 $38.39   3.262%   $39.6423   $39.64   $39.65   $39.60  
  Purchase #3 $141.81   12.351%   $159.325   $159.33   $159.35   $159.30  
  Purchase #4 $243.36   12.156%   $272.9428   $272.94   $272.95   $272.90  
  Purchase #5 $58.54   7.794%   $63.1026   $63.10   $63.10   $63.10  
  Purchase #6 $227.85   13.644%   $258.9379   $258.94   $258.95   $258.90  
  Purchase #7 $103.62   8.206%   $112.1231   $112.12   $112.10   $112.10  
  7 purchase totals = $998.54       $1,108.7231   $1,108.72   $1,108.75   $1,108.50