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 $27.25   7.502%   $29.2943   $29.29   $29.30   $29.30  
  Purchase #2 $90.73   3.215%   $93.647   $93.65   $93.65   $93.60  
  Purchase #3 $125.94   9.658%   $138.1033   $138.10   $138.10   $138.10  
  Purchase #4 $26.59   3.533%   $27.5294   $27.53   $27.55   $27.50  
  Purchase #5 $205.57   3.407%   $212.5738   $212.57   $212.55   $212.60  
  Purchase #6 $215.29   9.350%   $235.4196   $235.42   $235.40   $235.40  
  Purchase #7 $98.48   6.424%   $104.8064   $104.81   $104.80   $104.80  
  7 purchase totals = $789.85       $841.3738   $841.37   $841.35   $841.30