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 $41.98   9.571%   $45.9979   $46.00   $46.00   $46.00  
  Purchase #2 $145.27   5.483%   $153.2352   $153.24   $153.25   $153.20  
  Purchase #3 $176.67   11.406%   $196.821   $196.82   $196.80   $196.80  
  Purchase #4 $201.29   3.646%   $208.629   $208.63   $208.65   $208.60  
  Purchase #5 $220.53   4.228%   $229.854   $229.85   $229.85   $229.90  
  Purchase #6 $67.83   12.816%   $76.5231   $76.52   $76.50   $76.50  
  Purchase #7 $238.27   12.358%   $267.7154   $267.72   $267.70   $267.70  
  7 purchase totals = $1,091.84       $1,178.7756   $1,178.78   $1,178.75   $1,178.70