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 $30.47   13.642%   $34.6267   $34.63   $34.65   $34.60  
  Purchase #2 $223.50   12.496%   $251.4286   $251.43   $251.45   $251.40  
  Purchase #3 $118.63   5.866%   $125.5888   $125.59   $125.60   $125.60  
  Purchase #4 $152.41   13.449%   $172.9076   $172.91   $172.90   $172.90  
  Purchase #5 $233.46   5.467%   $246.2233   $246.22   $246.20   $246.20  
  Purchase #6 $212.96   5.662%   $225.0178   $225.02   $225.00   $225.00  
  Purchase #7 $117.38   3.424%   $121.3991   $121.40   $121.40   $121.40  
  7 purchase totals = $1,088.81       $1,177.1919   $1,177.20   $1,177.20   $1,177.10