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 $149.66   5.407%   $157.7521   $157.75   $157.75   $157.80  
  Purchase #2 $32.52   3.705%   $33.7249   $33.72   $33.70   $33.70  
  Purchase #3 $64.30   9.337%   $70.3037   $70.30   $70.30   $70.30  
  Purchase #4 $245.39   11.745%   $274.2111   $274.21   $274.20   $274.20  
  Purchase #5 $246.58   5.415%   $259.9323   $259.93   $259.95   $259.90  
  Purchase #6 $175.54   3.505%   $181.6927   $181.69   $181.70   $181.70  
  Purchase #7 $65.91   5.390%   $69.4625   $69.46   $69.45   $69.50  
  7 purchase totals = $979.90       $1,047.0793   $1,047.06   $1,047.05   $1,047.10