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 $232.27   12.192%   $260.5884   $260.59   $260.60   $260.60  
  Purchase #2 $128.83   6.237%   $136.8651   $136.87   $136.85   $136.90  
  Purchase #3 $54.62   6.290%   $58.0556   $58.06   $58.05   $58.10  
  Purchase #4 $96.35   10.280%   $106.2548   $106.25   $106.25   $106.30  
  Purchase #5 $142.91   5.370%   $150.5843   $150.58   $150.60   $150.60  
  Purchase #6 $188.29   10.249%   $207.5878   $207.59   $207.60   $207.60  
  Purchase #7 $148.28   10.837%   $164.3491   $164.35   $164.35   $164.30  
  7 purchase totals = $991.55       $1,084.2851   $1,084.29   $1,084.30   $1,084.40