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 $50.36   5.114%   $52.9354   $52.94   $52.95   $52.90  
  Purchase #2 $152.26   7.404%   $163.5333   $163.53   $163.55   $163.50  
  Purchase #3 $224.57   8.336%   $243.2902   $243.29   $243.30   $243.30  
  Purchase #4 $232.49   6.488%   $247.574   $247.57   $247.55   $247.60  
  Purchase #5 $36.43   10.777%   $40.3561   $40.36   $40.35   $40.40  
  Purchase #6 $240.84   4.466%   $251.5959   $251.60   $251.60   $251.60  
  Purchase #7 $190.64   6.864%   $203.7255   $203.73   $203.75   $203.70  
  7 purchase totals = $1,127.59       $1,203.0104   $1,203.02   $1,203.05   $1,203.00