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 $171.86   13.249%   $194.6297   $194.63   $194.65   $194.60  
  Purchase #2 $120.32   12.603%   $135.4839   $135.48   $135.50   $135.50  
  Purchase #3 $102.73   13.621%   $116.7229   $116.72   $116.70   $116.70  
  Purchase #4 $147.86   13.148%   $167.3006   $167.30   $167.30   $167.30  
  Purchase #5 $218.73   6.356%   $232.6325   $232.63   $232.65   $232.60  
  Purchase #6 $242.59   6.719%   $258.8896   $258.89   $258.90   $258.90  
  Purchase #7 $46.76   11.211%   $52.0023   $52.00   $52.00   $52.00  
  7 purchase totals = $1,050.85       $1,157.6615   $1,157.65   $1,157.70   $1,157.60