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 $35.52   3.453%   $36.7465   $36.75   $36.75   $36.70  
  Purchase #2 $189.43   8.667%   $205.8479   $205.85   $205.85   $205.80  
  Purchase #3 $124.67   7.203%   $133.65   $133.65   $133.65   $133.70  
  Purchase #4 $202.46   10.205%   $223.121   $223.12   $223.10   $223.10  
  Purchase #5 $238.36   3.304%   $246.2354   $246.24   $246.25   $246.20  
  Purchase #6 $208.53   8.811%   $226.9036   $226.90   $226.90   $226.90  
  Purchase #7 $94.89   5.797%   $100.3908   $100.39   $100.40   $100.40  
  7 purchase totals = $1,093.86       $1,172.8952   $1,172.90   $1,172.90   $1,172.80