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 $61.46   6.847%   $65.6682   $65.67   $65.65   $65.70  
  Purchase #2 $211.65   9.566%   $231.8964   $231.90   $231.90   $231.90  
  Purchase #3 $186.82   8.705%   $203.0827   $203.08   $203.10   $203.10  
  Purchase #4 $77.67   4.185%   $80.9205   $80.92   $80.90   $80.90  
  Purchase #5 $120.62   9.870%   $132.5252   $132.53   $132.55   $132.50  
  Purchase #6 $46.37   13.492%   $52.6262   $52.63   $52.65   $52.60  
  Purchase #7 $9.44   7.132%   $10.1133   $10.11   $10.10   $10.10  
  7 purchase totals = $714.03       $776.8325   $776.84   $776.85   $776.80