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 $244.46   11.805%   $273.3185   $273.32   $273.30   $273.30  
  Purchase #2 $160.33   10.727%   $177.5286   $177.53   $177.55   $177.50  
  Purchase #3 $45.96   11.372%   $51.1866   $51.19   $51.20   $51.20  
  Purchase #4 $199.94   3.698%   $207.3338   $207.33   $207.35   $207.30  
  Purchase #5 $10.70   3.332%   $11.0565   $11.06   $11.05   $11.10  
  Purchase #6 $162.42   11.280%   $180.741   $180.74   $180.75   $180.70  
  Purchase #7 $141.79   13.502%   $160.9345   $160.93   $160.95   $160.90  
  7 purchase totals = $965.60       $1,062.0995   $1,062.10   $1,062.15   $1,062.00