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 $56.92   10.544%   $62.9216   $62.92   $62.90   $62.90  
  Purchase #2 $150.39   7.496%   $161.6632   $161.66   $161.65   $161.70  
  Purchase #3 $189.77   7.469%   $203.9439   $203.94   $203.95   $203.90  
  Purchase #4 $66.84   4.575%   $69.8979   $69.90   $69.90   $69.90  
  Purchase #5 $182.52   11.685%   $203.8475   $203.85   $203.85   $203.80  
  Purchase #6 $114.52   4.295%   $119.4386   $119.44   $119.45   $119.40  
  Purchase #7 $213.89   7.398%   $229.7136   $229.71   $229.70   $229.70  
  7 purchase totals = $974.85       $1,051.4263   $1,051.42   $1,051.40   $1,051.30