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 $93.49   11.574%   $104.3105   $104.31   $104.30   $104.30  
  Purchase #2 $10.80   7.838%   $11.6465   $11.65   $11.65   $11.60  
  Purchase #3 $125.82   13.144%   $142.3578   $142.36   $142.35   $142.40  
  Purchase #4 $177.95   7.660%   $191.581   $191.58   $191.60   $191.60  
  Purchase #5 $184.71   13.407%   $209.4741   $209.47   $209.45   $209.50  
  Purchase #6 $52.91   13.803%   $60.2132   $60.21   $60.20   $60.20  
  Purchase #7 $232.68   6.372%   $247.5064   $247.51   $247.50   $247.50  
  7 purchase totals = $878.36       $967.0895   $967.09   $967.05   $967.10