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 $239.53   9.343%   $261.9093   $261.91   $261.90   $261.90  
  Purchase #2 $91.35   7.254%   $97.9765   $97.98   $98.00   $98.00  
  Purchase #3 $108.31   11.704%   $120.9866   $120.99   $121.00   $121.00  
  Purchase #4 $24.65   3.530%   $25.5201   $25.52   $25.50   $25.50  
  Purchase #5 $243.89   6.589%   $259.9599   $259.96   $259.95   $260.00  
  Purchase #6 $62.87   4.708%   $65.8299   $65.83   $65.85   $65.80  
  Purchase #7 $184.76   11.492%   $205.9926   $205.99   $206.00   $206.00  
  7 purchase totals = $955.36       $1,038.1749   $1,038.18   $1,038.20   $1,038.20