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 $50.79   3.270%   $52.4508   $52.45   $52.45   $52.50  
  Purchase #2 $197.84   3.821%   $205.3995   $205.40   $205.40   $205.40  
  Purchase #3 $236.77   12.444%   $266.2337   $266.23   $266.25   $266.20  
  Purchase #4 $85.37   11.405%   $95.1064   $95.11   $95.10   $95.10  
  Purchase #5 $244.94   3.507%   $253.53   $253.53   $253.55   $253.50  
  Purchase #6 $77.89   12.229%   $87.4152   $87.42   $87.40   $87.40  
  Purchase #7 $168.26   9.319%   $183.9401   $183.94   $183.95   $183.90  
  7 purchase totals = $1,061.86       $1,144.0757   $1,144.08   $1,144.10   $1,144.00