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 $206.92   11.612%   $230.9476   $230.95   $230.95   $230.90  
  Purchase #2 $21.61   5.645%   $22.8299   $22.83   $22.85   $22.80  
  Purchase #3 $149.81   7.496%   $161.0398   $161.04   $161.05   $161.00  
  Purchase #4 $145.57   5.290%   $153.2707   $153.27   $153.25   $153.30  
  Purchase #5 $152.74   12.677%   $172.1028   $172.10   $172.10   $172.10  
  Purchase #6 $205.29   10.319%   $226.4739   $226.47   $226.45   $226.50  
  Purchase #7 $78.53   4.442%   $82.0183   $82.02   $82.00   $82.00  
  7 purchase totals = $960.47       $1,048.6830   $1,048.68   $1,048.65   $1,048.60