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 $221.85   6.308%   $235.8443   $235.84   $235.85   $235.80  
  Purchase #2 $158.84   13.743%   $180.6694   $180.67   $180.65   $180.70  
  Purchase #3 $23.64   3.715%   $24.5182   $24.52   $24.50   $24.50  
  Purchase #4 $211.63   5.711%   $223.7162   $223.72   $223.70   $223.70  
  Purchase #5 $232.76   7.810%   $250.9386   $250.94   $250.95   $250.90  
  Purchase #6 $93.53   5.523%   $98.6957   $98.70   $98.70   $98.70  
  Purchase #7 $246.59   5.341%   $259.7604   $259.76   $259.75   $259.80  
  7 purchase totals = $1,188.84       $1,274.1428   $1,274.15   $1,274.10   $1,274.10