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 $184.87   3.275%   $190.9245   $190.92   $190.90   $190.90  
  Purchase #2 $138.54   7.336%   $148.7033   $148.70   $148.70   $148.70  
  Purchase #3 $60.63   5.282%   $63.8325   $63.83   $63.85   $63.80  
  Purchase #4 $187.27   12.771%   $211.1863   $211.19   $211.20   $211.20  
  Purchase #5 $95.90   11.492%   $106.9208   $106.92   $106.90   $106.90  
  Purchase #6 $118.42   6.551%   $126.1777   $126.18   $126.20   $126.20  
  Purchase #7 $49.98   7.825%   $53.8909   $53.89   $53.90   $53.90  
  7 purchase totals = $835.61       $901.6360   $901.63   $901.65   $901.60