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 $213.35   9.140%   $232.8502   $232.85   $232.85   $232.90  
  Purchase #2 $166.66   11.667%   $186.1042   $186.10   $186.10   $186.10  
  Purchase #3 $157.70   10.794%   $174.7221   $174.72   $174.70   $174.70  
  Purchase #4 $218.37   11.634%   $243.7752   $243.78   $243.80   $243.80  
  Purchase #5 $16.75   4.358%   $17.48   $17.48   $17.50   $17.50  
  Purchase #6 $160.71   11.410%   $179.047   $179.05   $179.05   $179.00  
  Purchase #7 $61.52   6.505%   $65.5219   $65.52   $65.50   $65.50  
  7 purchase totals = $995.06       $1,099.5006   $1,099.50   $1,099.50   $1,099.50