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 $197.46   4.423%   $206.1937   $206.19   $206.20   $206.20  
  Purchase #2 $191.79   10.814%   $212.5302   $212.53   $212.55   $212.50  
  Purchase #3 $141.67   8.349%   $153.498   $153.50   $153.50   $153.50  
  Purchase #4 $67.61   13.301%   $76.6028   $76.60   $76.60   $76.60  
  Purchase #5 $120.79   8.818%   $131.4413   $131.44   $131.45   $131.40  
  Purchase #6 $55.93   3.843%   $58.0794   $58.08   $58.10   $58.10  
  Purchase #7 $220.31   6.214%   $234.0001   $234.00   $234.00   $234.00  
  7 purchase totals = $995.56       $1,072.3455   $1,072.34   $1,072.40   $1,072.30