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 $84.71   10.856%   $93.9061   $93.91   $93.90   $93.90  
  Purchase #2 $102.61   12.714%   $115.6558   $115.66   $115.65   $115.70  
  Purchase #3 $232.96   10.198%   $256.7173   $256.72   $256.70   $256.70  
  Purchase #4 $246.71   12.496%   $277.5389   $277.54   $277.55   $277.50  
  Purchase #5 $45.92   7.652%   $49.4338   $49.43   $49.45   $49.40  
  Purchase #6 $100.67   4.595%   $105.2958   $105.30   $105.30   $105.30  
  Purchase #7 $168.93   6.146%   $179.3124   $179.31   $179.30   $179.30  
  7 purchase totals = $982.51       $1,077.8601   $1,077.87   $1,077.85   $1,077.80