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 $194.52   3.120%   $200.589   $200.59   $200.60   $200.60  
  Purchase #2 $205.53   13.334%   $232.9354   $232.94   $232.95   $232.90  
  Purchase #3 $34.25   12.469%   $38.5206   $38.52   $38.50   $38.50  
  Purchase #4 $168.64   9.446%   $184.5697   $184.57   $184.55   $184.60  
  Purchase #5 $83.53   6.512%   $88.9695   $88.97   $88.95   $89.00  
  Purchase #6 $164.70   13.122%   $186.3119   $186.31   $186.30   $186.30  
  Purchase #7 $6.52   9.540%   $7.142   $7.14   $7.15   $7.10  
  7 purchase totals = $857.69       $939.0381   $939.04   $939.00   $939.00