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 $179.66   10.458%   $198.4488   $198.45   $198.45   $198.40  
  Purchase #2 $250.65   4.422%   $261.7337   $261.73   $261.75   $261.70  
  Purchase #3 $211.67   11.153%   $235.2776   $235.28   $235.30   $235.30  
  Purchase #4 $44.57   10.811%   $49.3885   $49.39   $49.40   $49.40  
  Purchase #5 $210.85   13.244%   $238.775   $238.78   $238.80   $238.80  
  Purchase #6 $70.43   12.619%   $79.3176   $79.32   $79.30   $79.30  
  Purchase #7 $43.96   9.580%   $48.1714   $48.17   $48.15   $48.20  
  7 purchase totals = $1,011.79       $1,111.1126   $1,111.12   $1,111.15   $1,111.10