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 $58.76   3.332%   $60.7179   $60.72   $60.70   $60.70  
  Purchase #2 $24.27   9.801%   $26.6487   $26.65   $26.65   $26.60  
  Purchase #3 $130.91   12.561%   $147.3536   $147.35   $147.35   $147.40  
  Purchase #4 $125.65   4.547%   $131.3633   $131.36   $131.35   $131.40  
  Purchase #5 $223.98   9.798%   $245.9256   $245.93   $245.95   $245.90  
  Purchase #6 $36.92   6.612%   $39.3612   $39.36   $39.35   $39.40  
  Purchase #7 $182.25   10.154%   $200.7557   $200.76   $200.75   $200.80  
  7 purchase totals = $782.74       $852.1260   $852.13   $852.10   $852.20