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 $167.90   11.108%   $186.5503   $186.55   $186.55   $186.60  
  Purchase #2 $135.52   5.158%   $142.5101   $142.51   $142.50   $142.50  
  Purchase #3 $63.44   7.187%   $67.9994   $68.00   $68.00   $68.00  
  Purchase #4 $213.59   5.453%   $225.2371   $225.24   $225.25   $225.20  
  Purchase #5 $143.37   11.302%   $159.5737   $159.57   $159.55   $159.60  
  Purchase #6 $220.33   5.755%   $233.01   $233.01   $233.00   $233.00  
  Purchase #7 $28.86   6.272%   $30.6701   $30.67   $30.65   $30.70  
  7 purchase totals = $973.01       $1,045.5507   $1,045.55   $1,045.50   $1,045.60