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 $91.25   10.854%   $101.1543   $101.15   $101.15   $101.20  
  Purchase #2 $137.30   11.481%   $153.0634   $153.06   $153.05   $153.10  
  Purchase #3 $151.39   6.694%   $161.524   $161.52   $161.50   $161.50  
  Purchase #4 $220.73   5.562%   $233.007   $233.01   $233.00   $233.00  
  Purchase #5 $192.59   11.399%   $214.5433   $214.54   $214.55   $214.50  
  Purchase #6 $205.26   6.351%   $218.2961   $218.30   $218.30   $218.30  
  Purchase #7 $24.74   10.702%   $27.3877   $27.39   $27.40   $27.40  
  7 purchase totals = $1,023.26       $1,108.9758   $1,108.97   $1,108.95   $1,109.00