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 $62.52   9.618%   $68.5332   $68.53   $68.55   $68.50  
  Purchase #2 $204.28   6.713%   $217.9933   $217.99   $218.00   $218.00  
  Purchase #3 $206.60   12.152%   $231.706   $231.71   $231.70   $231.70  
  Purchase #4 $68.35   9.850%   $75.0825   $75.08   $75.10   $75.10  
  Purchase #5 $120.60   10.473%   $133.2304   $133.23   $133.25   $133.20  
  Purchase #6 $247.60   12.529%   $278.6218   $278.62   $278.60   $278.60  
  Purchase #7 $210.78   9.836%   $231.5123   $231.51   $231.50   $231.50  
  7 purchase totals = $1,120.73       $1,236.6795   $1,236.67   $1,236.70   $1,236.60